I watched a groundhog climb over my 7 foot trellis last year.

Groundhog proof seems to be a whole echelon above critter proof.

~emmers

I thought about that but a ground hog would have left tracks and I doubt one could reach the tall buds on the zucchini plants without either folding over a few leaves or the flower stalks themselves. The buds are cut off almost right at the blossom, maybe a 1/4" down and no signs of the blossom on the ground.
The dirt around the lettuce is raked smooth, even robbins leave tracks in it. It wasn't disturbed at all.

I did find quite a few earwigs when I pulled up my early pea plants, but the lettuce damage is too severe and too fast. It looks more like a deer took a big bite out of each head but I've never seen any deer this far into town and again, no tracks.

The way I've got the fence set up the top and bottom curl outward a good foot or so. I even doubled the fence since I had small rabbits pushing themselves through it. I ran a 24" tall section of rat wire with 1/4" holes around the lower part at the ground.

That sounds like a better version of my new fence :)

I took 6 feet of chickenwire and bent several inches outward at the bottom and secured it with a run of paver blocks (too lazy to bury it) and left the top foot or so floppy. It's held up so far against the marauding hordes (except for squirrels and chipmunks of course) but I'm pretty sure the groundhog could get in if it wanted to.

My first line of defense is not letting it know that there's goodies in the garden. My 'hog troubles last year started when I foolishly left the garden door open to (I thought) allow the 3 baby bunnies that got in a chance to escape. Instead I ended up needing to chase a groundhog and three baby bunnies out of the garden - and herding baby bunnies is no easy task - and for the rest of the season the groundhog treated the garden like an all-you-can-eat buffet.

He did seem to like the squash, and the groundhogs in my yard can go up on their hind legs to nibble something tasty...

But considering the lack of tracks you do seem to have a puzzle on your hands - flying deer? Levitating groundhog? I don't think a bird would do what you're describing on your lettuce.

Hope it was a passing fancy and won't become a repeated offense.

~emmers

I pretty much ruled out anything that can leave foot prints. I've gone so far as to sweep the area with a broom to be sure prints are left. The lettuce looks like it's been bitten off from the side, with all the plants in the aisle being hit, with the exception of one in the back of the patch with some nibbling off the now bolting leaves on top.
I measured the blossoms that were cut off, their 20" tall. My Zucchini plants are nearing 5' tall right now, only the one plant, directly across from the lettuce at the end of two adjacent rows have been affected.
I have several traps set for groundhogs, with lettuce, so far all I got was two very large rabbits, neither of which were capable of getting in with out leaving foot prints.
I did find a few earwigs, but have never had damage due to those, but to be sure I dusted for them today. I also set a game camera in the garden. If its large enough to trigger the camera, I'll know what it is soon enough. I removed the eaten lettuce plants.
I would also think that if it were a groundhog, I'd see damage to my red beets, squash, melons, cantaloupes, etc. Not to mention some sort of tracks.
I haven't seen a deer in this area for 20 years, its just to densely populated and either way the neighbors dog or any one of my cats here would have chased it off. I've got one huge cat that loves fresh rabbit, its not often one gets near the garden without either a chase or becoming a gut pile in the grass.
The round holes in the ground puzzle me, I don't see any mole hills, we generally don't have any snakes, and filling in the holes only lasts to the next morning. In several years now, I've not yet found the critter that made them.
The cats drag in mice, chipmunks, rabbits, moles, voles, and on occasion a groundhog.
The neighbor had a few burrowing under his shed, they died of lead poisoning last month, so far the holes haven't been re opened. We all look pretty hard to find new burrows, and take turns stalking them.
I did shoot one last month that was able to stand almost 30" tall on his hind legs trying to look over the neighbors garden fence, but that was the last time he stuck his head up anywhere. The shot turned him into a fuzzy Pez dispenser.

Hopefully the game cam catches something tonight.

The round holes might be chipmunks? There are several of those in our lawn, and we see the chipmunks dart right in. It surprised me they were so out in the open in the lawn.

The vole holes in my garden were smaller, more like one inch diameter than two.

Hope your surveillance pays off.

~emmers

The holes sound like rat holes. If it is, your game cam will catch them.

Well, I came home today and found 90% of the lettuce chewed off to the ground, all of my leaf lettuce is gone, and one whole row of squash is trampled and chewed.
The game came found the culprit, a HUGE ground hog, who visited at 9:57AM, and again at 4:37PM.
The came shows him dropping into view, he didn't trip the camera til he had eaten quite a bit. There are no holes under the fence. He's got to be scaling the fence and jumping in. He never once touched the open aisle, he stayed in the lettuce, never letting his feet touch the dirt inbetween. He never left a track. The lettuce heads are 14" tall, with some starting to bolt, his back is higher than those. He's one fat critter. I left him a huge bait pile of easy to get at lettuce and apples, if he survives that I'll have to sit for him with a rifle. If the bait pile gets him, He's in for the ride of his life. I also set a half dozen traps in and around the garden.
The part that gets me is that he scaled a 6' fence, with a 14" outward and downward overhang. I'd have trouble getting over that fence.
I also found that he chewed through the adjacent shed, there's a 24" hole in the one wall, he chewed through the back wall, then tried to chew through the garden side wall to get at the garden. I had a problem years ago with chipmunks chewing through the garden side wall years ago and I doubled the T111 siding with a layer of sheet metal in between. I guess hee hit the sheet metal and gave up.
The bad part is he not only got at my garden, but he's eaten up both neighbor's gardens, with the exception of one, who has no fence.

Another neighbor said she noticed that all her newly planted flowers were eaten this morning as well.
Tonight I put a rifle at each back window of the house, if the bait pile surprise don't get him, some lead will.
If he's as big as he looked in the game cam, he's pushing 30lbs or more.

I don't know if, for the sake of science and stronger fences, you'd be willing to let him make one more foray into the garden so that you could point your cam at the fence and see how he's getting over - I'd be interested to know, because I'll have the same problem if the 'hog who was wandering through the yard yesterday decides to see what's in my garden.

A last meal for the condemned, and for the advancement of groundhog exclusion technology?

Nice sleuthing!! Who knew they were so stealthy, and emmers called it.

Now, good luck getting rid of the varmit!

The fence is just over 6' tall, the bottom of the fence is double and triple in some places with sheet metal buried well below the end of the fence. Digging under is just short of impossible unless he can eat through aluminum sheet metal and wire fence. The fence is three sided, bordered on the north west corner by a 10x15 wooden shed on an 8" think concrete slab. The lettuce is along the shed wall in 6 narrow rows about 20' long. So far he's eaten 3 rows down to the ground and never left a foot print in the aisle or dirt. His fir and tail must smooth over his foot prints. I left a huge bait pile of lettuce, broccoli, and cantaloupe yesterday, and sat waiting, he never touched it.
I sat and watched the garden till about noon, went in for a bite to eat and came out 15 minutes later and 15 heads of lettuce were chewed off and no sign of the hog.
I gave some thought to him maybe climbing over the shed and dropping in from the roof, but that wouldn't let him out. The fence is supported with poles about half way, so it won't support much weight hanging on it. Let alone a ground hog trying to climb over the outer overhang to get in.
I did find some chewing on the adjacent shed today, but he gave up, and there's some digging around the edge of the garage on one corner but again, he hit the rough concrete over pour about 6" down and gave up.
I have 6 live traps set, a dozen various size conibear traps set in among the remaining lettuce. So far he's not touched a trap. I dusted the surrounding area with cayenne pepper powder, figuring if he walks in it and licks it off, he's in for a surprise. I'm not sure if ground hogs are affected the same as we are by hot peppers?
Also in the garden are various other sprouts, okra, new squash plants, onions, and melons but he's only gone after the lettuce and zucchini blossoms so far.
If I catch the thing, will stringing up a dead one ward off others?
I've combed all over the neighborhood and have yet to find a den or burrow, if I find his home, I know where to wait for him. At work, we've had a number of ground hogs burrow under the store room floor, but its just a matter of sitting and waiting for the hog to show his head and bang, he's gone.

How about a trap - like what is used for raccoons? We have caught many a raccoon with something similar to the link below.

Hi everyone - I am new to gardenweb - I really appreciate all the advice here. :-)

(USDA Zone 7b)

Here is a link that might be useful: Havahart 1 Door Raccoon Trap

I can't believe he ate 15 heads of lettuce in 15 minutes! He must be watching you while you're watching for him! I wish I could provide some advice but it sounds like you're trying pretty much every possible option already.