Ok, I gave up trying to grow a garden in the presence of gophers/ground squirrels. I live in the woods and it would be impossible to kill them all. There is an entire metropolis under my garden. I had three beds raised on stacks of pallets. I put metal collars on them and that helped, although the game camera, at night, caught a large rabbit in one.
Following the "up is good" theory I started adding bathtubs set on cement blocks and that also works well, so far. In a hoop house I plant my tomatoes in stacks of tires, also with metal collars. The sheet metal isn't cheap but the tubs come from salvage yards and can be had for next to nothing. I think that I will try cardboard collars to see if the evil rodents can, or will, climb them.
Last year I began doing a little hugeculture by putting dried brush in the tub bottoms and adding dirt, chicken straw and compost. Even with the heat I seem to be watering less.
I don't see any ground squirrels this year. I hope that they've given up and gone home. This year is better for the garden overall, we got a better start than last year and even though it's hot hot hot the plants are coming on. I will say that it's taken far longer than it should have to outsmart the critters. They were just doing what came naturally and I wasn't.
On a related note, a few years ago I hauled home, from a yard sale, an old utility tub. I noticed that things planted in it, even sunflowers, didn't do well. This year everything I planted in it just flat out died. Same dirt, good drainage, same compost. I've decided that this is just a toxic tub. It must be made of something that is leaching into the dirt and poisoning plants. Something else to consider as we build our gardens.