@Raincityrider, I have a Rodenator. It’s loud, you run out of gases really fast, and it doesn’t really kill much–just collapses the tunnel. Maybe if you were really diligent with it, you would see results, but Mr. Suspiria only ever used it once and then got bored and wandered off. And me, actual Suspiria, isn’t going to voluntarily stand near a gas explosion, even a small one.
OP, i also moved to a pocket gopher infested acreage about 5 years ago. I had my local farm service company come out and poison my fields but I would not recommend that either. The machine they used essentially cut big furrows in the field, dropped strychnine-soaked grain, and then covered the tunnels back up. I was not worried about the strychnine because it takes a ton of that stuff to affect a horse even if they did dig down to it, which they did not. However, the tunnels left by the machine were even deeper and more annoying than the gopher tunnels.
I agree with the poster who said the problem will take care of itself because the gophers really seem to dislike the concussion from horses walking around up top. Now I only go after the ones who set up shop on my lawn. Mr Suspiria likes trapping them but you will never get them all that way. I use poison. I probe the big mounds with a long screwdriver til I find a tunnel, and then dig down into the tunnel and cram a block or two of gopher poison (like D-Con, but brown) and cover the tunnel back up. Pocket gophers seldom come above ground so I have never had a problem with a neighbor dog or cat eating a poisoned gopher.