One thing that I found that will work with gophers is . . . harassment.
When I first began growing potatoes again after about 20 years - vole attack then - a gopher moved in on my little patch. I'd only planted about 10sqft so he was going to make quick work of them!
I went out with a thin metal rod that was about 30 inches long, my leather gloves and a hammer. I drove that rod in every few inches all around and under that little bed of potatoes. Must have spent an hour doing it. I mean, it went in at every angle! There was no doubt in my mind that I hit his burrow in several places. (Truth be known, I checked the rod a few times for gopher blood . . . just hoping :/.)
He left. I have no idea where he went (up, down or sideways) but at that garden location, there were quite a few gopher mounds in the near area.