OK, Lets look at a few things. Are you the only house in the area? Is you yard an open grass area? Forget about keep the rodents out with a fence, but you could use small mesh hardware cloth of say 24 inch width around the bottom of your fence, maybe buried several inches into the ground. Snakes can climb, but if the top were bent out you would most likely defeat any attempt to crawl over. Do you have a pet, a dog or cat? Sometimes they will deter snake entry. I have a medium sized cat and I am told that the area were I live was copperhead heaven when I moved in and I have brush growing with 10 feet of my place and I have yet to see a snake of any kind and I think that the cat might have something to do with it. I know that she catches mice and chipmunks because she brings them into the house and lets them loose to chase.
You live in CA and I would guess your days are hot and sunny. Remember NO SNAKE is going to come out in the sun during the day. They are most active in the early morning and late afternoon. When it get cold at night they don't move much.
I grew up in SouthWest Florida in a subdivision called Pine Ridge, but it was really rattlesnake heaven and in all the time we lived there we only had one rattler get up to the house and my father killed that one.
At 19 I was struck by one, a big one, but was lucky.
Ask your local Fish and Game boys what they recommend.
BTW, how did you encounter yours?

1eyedJack and the Dawg

None of teh snake deterents work, especially not the ultra sound emitting silliness. They sell that stuff playing on peoples intense fears.

But you should know - you moved into their home.

Just walk through your garden and yard before getting to work. If snakes aren't there they won't come in with your activity present. Snakes just want to be left alone.

People all across the world live with snakes in their yards, and in their fields that they work in daily - usually with bare legs and feet. They're just pretty easy to spot and avoid.

If you see one in your yard just grab a broom and gently encourage it to move away.

joe

ole dawg
i dont mean to disagree here but who on earth told you snakes dont like coming out in the sun????????
snakes come out in the sun and heat to warm up. they are cold blooded. they need heat to keep their blood circulating. rattlers are no exception. i live in ontario. right now the snames are curled up sound a sleep and wont awake until spring if they are lucky. we have massassauga rattlers all around up here and they can often be seen in the warm weather sunning themselves on rocks trying to store some of the heat

I was raised on a farm remote from any town and our yard was near a mix of pasture, woods, and a creek - all the ingredients for snake haven. We had a one acre yard and vetable garden. This was kept snake free becasue we kept one to two dogs outside the house, but within the fenced yard. The dogs has free run of this enclosure. The main reason for the fence was to keep the cows and chickens out of the yard and garden. The dogs did the remainder of policing. About only varmit the dogs did not keep out was moles.

Common snakes to this area were water mocassin, cotton mouth, black snake, several garters, and blue racers. The blue racers were the most fun of all. When these critters are warmed up, they are at least twice as fast as other snakes and luckily are realtively harmless - they avoid approaching humans. Their speed is very startling, however, causing one to miss a heart beat or two when first surprised by one. Blue racers are excellent tree climbers and can race through a tree top so vigorously to cause the tree crown to shake.

I saw the statement about the sun too. Perhaps he meant in more intense heat which is true. But snakes love to bask so unless the sun has heated surfaces above 90 degrees, I would expect to see them out. They may be more active with hunting in the morning and late afternoon/early evening.

One thing to keep in mind is to keep a clean yard clear of wood piles, tin, building supplies and places that would allow them to feel secure and not right out in the open exposed. Plus those places also allow there prey to feel secure and provide hiding spots(also bushes against the side of the house). If you are experiences a drought and your watering your lawn, you may be providing a source of water for them and there prey. Snake repelling agents don't work from what I've heard. Your taking over their habitat. Hopefully you have time to have animal control remove them rather than killing them.