My local squirrels don't seem to have touched my garden, so I've left them be. Same with the opossum (apparently they not only eat snails, slugs, spiders, cockroaches, rats, mice and snakes--when around humans they also eat trash--seems quite symbiotic, even "green"). I did have an awful rabbit problem though, with my landscaping especially (even though the landscape design was supposedly all rabbit-proof plants). Since rabbits are lazy creatures, for the garden all it took was a wire fence a couple feet high. But for the landscaping, no way to fence that in. Drove me absolutely batty. Tried all sorts of things, long story short, a quiet and powerful .22 pellet rifle was effective (and to the best of my knowledge, my neighbors are none the wiser).
If that isn't an option for you, I'd suggest something that didn't work for my rabbit problem. I tried putting out rat poison pellets in my back yard, it is a blood thinner that causes them to get lethargic, and eventually go to sleep and not wake up. Vitamin K is a quick and effective antidote for pets or people if there were ever an accident, although I probably wouldn't have tried it if there were pets or little kids frequenting my back yard, since it's quite possible a dog or cat could die before they figured out what the problem was. Mixed it with bananas or apples, which some people said the rabbits would then eat. The problem I had is that the squirrels always ate it first...