Gasoline works!
https://www.youtube.com/watch?v=uNbQkZ7B3QE
Seriously though, at my last house we had 8000 sq ft of lawn and the soil was very conducive to gophers. My rottie was destructively trenching the place trying to get them so I decided to teach her how to team hunt gophers and it became a fun game every spring as we collected dozens of them.
She would alert-bark whenever there was a new interloper with fresh diggings. I would bring over the garden hose and run water down while also feeding in the pile of fresh dirt. This would raise the water level in the tunnels and always bring the varmint to the surface for a breather hole. She would hear them coming to the surface and point, I would put water on the spot and up popped the gopher. She would grab it, give it the death bite, and place the kill at my feet waiting for praise and a treat. The whole process usually took 5-10 minutes and was 95% effective. Only a very rare time did a gopher escape the team hunt. This was a fun game we played for many years during gopher season and she probably got 200 of them. Best dog ever!
Turning lemons into lemonade.