OK take it from a professional, Owls and Gopher snakes are a good start, BUT a preemptive strike is best, if you can plan your garden ahead of time to have both above ground and bellow ground chicken wire, You will be off to a good start, Gopher purge is only good in the areas it grows and is a semi-myth, Sonic devices have failed completely when I tried them and have varying results based on soil type (clay or sand), I have had good success in running them away from their den’s with a high pressure water hose on their hole, but this works in compacted (non raised bed) soil and not effective at all if the Gopher has been there for a few weeks. The hands down best thing I know of is to put them into the food chain again with a loyal loving Cat- but watch out for Frogs /lizards / and birds as cats are non descriminate. – bottom Line, there are no easy way to get gophers, traps and bait still seem to be the most popular and most non-ecological solution. I did see a great Blue Herron in our gopher fields many seasons plucking gophers out of their holes, throwing them in the air and swalloing them whole, as if it was a fish. Very good nature show there. For me I simply overplant everything and hope for the best.
I suggest trying a combination of hot pepper spray and caster oil. I’ve never had this problem so I’m simply passing on something I’ve read.