Don't shoot that squirrel! Grey squirrels and some others are legally
protected in California. Even legally protected species may be trapped and
their numbers "thinned" if they are a threat to your livelihood. Call your
local Fish and Game guys for a permit.
I got the idea that you would prefer not to kill the critters. In that case,
you will need to provide a barrier between your planted areas and the
bushy-tailed ones. A fence that goes underground for a couple of feet and
stands eight feet above the ground will do double duty for both squirrel and
deer. You may need to use avian hardware cloth to get holes small enough
that the little guys don't go through it. The top of it will need to have a
return curled to the outside. The underside of needs to be smooth so the
squirrels can't climb around it. Use the same idea as a squirrel barrier on
a bird feeder.
Please don't try to trap and release. You probably won't eliminate damage to
your plantings and the extra nutrition you provide will increase the
human-trained critter population your neighbors will have to deal with.
Full Circle Organic Farm