I know that there are sprays that are supposed to deter dogs so maybe check a pet store and see if their is stuff for cats.
And I know that there are plants that are as attractive as catnip to cats . I learned that from 'The gardener guy" . Maybe look into planting a patch of that stuff to deter the cat away from the feeders.

Here is what I do to deter cats from my flower garden.

-1/2 pound serrano peppers
-Lemon Juice
-Vinegar
-32ounce spray bottle

Process the serranoes in a food processor. Take the mush and squeeze out any and all juice and save it.
Then let the mush dry for a few days until it has hardenned. After you have dried the serrano mush use coffee filters and encase the hardenned mushed in the filters, basically I made tea bags.
Then I brewed "serrano tea". After that, mix the tea and fresh serrano juice and pour it into half of a 32ounce sprayer. Fill the remainder of the sprayer with half lemon juice and half vinegar.
I sprayed it in the garden where the cats like to go and now the cats don't go there.
Be sure and label your leftover stuff and put it in the refrigerator.

Mike

Be sure and let the other people in the house know what you are up to. My wife mistook the mush for guacamole and dipped a chip in it. She does not like spicey food so you can form your own opinion as to how things went!

In the kindnest way I can put this..cats dont belong outside. Not good for the cat, not good for the wildlife. If you cant bring it inside...find it a nice home that can. I get VERY UPSET when my neighbors allow their cats to wander and they end up on my property killing my birds.If the cat is messing up you garden...immagine the anger your neighbors have when your cat violates theirs. Not the cats fault...it's the owner. Please dont be a bad cat owner.

You can try burying moth balls just an inch below the soil. It won't harm your plants. I've done this with my houseplants when kitties tried to use large planters as litter box.

Cats and birds do not mix. I don't have outside cats for that reason. A cat can catch a hummingbird. One day your cat may be bringing you one and dropping it at your feet. It may not even be dead but so badly injured that it will not recover and then you will have to deal with it. There is no way to keep cats away unless you keep them confined as they are natural predators. I know that you were hoping for a better solution.

Penny

Over years of gardening, people have asked me what kinds of poisons to use to get rid of cats that were "going" in their gardens and vegetable beds and lurking around bird feeders. I think many cat lovers don't understand the lengths some folks will go to. It's safest to keep them indoors if you can't be sure they'll stay in your yard.

Cats like to go on fluffy dry soil so keeping the soil moist may deter them. I've also emptied old spice containers (ground cloves, cumin, cinnamon, garlic, etc) on bare areas and it has deterred the tom that was spraying in my yard, but I'm sure he just moved to the next house. I think pepper-based stuff might hurt your kitty's eyes & nose but if it's diluted enough it may be ok.

I watched my neighbor's fat lazy cat jump five feet straight up from a crouched position to grab a hummer at a feeder, so make sure you hang them high enough. (I didn't think he could it but he did.)

I have outside cats only because a mother cat and her four kittens adopted us. Since I could not find homes for them and didn't want them all in the house, we made a nice cat house outside for them and had all five (including the mother cat)fixed. We live in the country and we have had them for five years. Humane societies are overrun with unwanted cats. So instead of adding to their population, we took responsibility for this mother cat, gave them a home with food & water every day and shelter. Yes, cats will catch birds and other wildlife and you will have unfortunate casualties. However, we also have hawks that prey on our hummers and wild birds. We try to hang our hummingbird feeders up high because of the cats. I've read to put a collar with a bell on them to warn birds of their presence. However, they just seem to pull the collars off. Since they are now adult cats, they roam the fields and return with rats, mice and voles. I am thankful they do this. Also, when they were smaller and tended to stay home, I put out a large litter box for them. I used a large plastic container I got at Wal-Mart and cut a hole in the side. They used it instead of my flowers on most occasions. Just a few ideas of what we did and why we don't keep them in the house.

We let our cats out in our back yard which is fenced in and they can't get out. We only put the hummer feeders off the deck or on very high poles that the cats can't get to.

I wouldn't worry about the ammonia in your veggie garden. The amount is not enough to harm the plants unless your cat is spraying on them. Actually urea is a good fertilizer. Just make sure to keep the plants well watered. There isn't much you can do to keep them from digging in the soft soil. It's what they do. Mine always go in the bed I just finished tilling. They haven't killed anything in there yet.

I had read that feeders have to be no more than about 5ft high. I have one hung under a roof that is about that height, but I worry that some of the resident outside cats might scare the hummers away. I'm getting a second feeder and will try putting it up higher. BTW I have 4 inside cats and one of them spotted a hummer the first time one came to my feeder.

There are outside cats in my neighborhood. I also am lucky enough to have a fairly high volume of hummers in my yard during the breeding season. Even though cats will notice the hummers in my yard they seem happy to go to the field across the street and come back with mice , voles etc. Once in a while I will find one lurking in my main garden but I make a plain they are not welcome and when they see me they are gone in a flash. So far I have not seen any dead hummer in my yard or remnants of one but I suppose it is inevitable it will happen. Cats are hunters.