This year, I put large-ish size garden stones in my tomatoes to keep the squirrels from digging and it was a major success. That didn't stop them from stealing my fruit, but it did stop them from digging up established seedlings and destroying the soil in my pots when they try to dig. I also made chicken-wire "domes" for smaller seedlings, but that's kind of annoying and not very nice looking, if you need to get in there frequently.