Most pros poison them, but we have lots of pets in our area so I don’t like to use poisons. I trap them with a gopher trap (the kind with spring loaded spikes that drive into their head to kill them, it’s gruesome but very effective.) Place a rope on the trap and tie the other end to a stake. Dig a 12″ diameter hole to expose a tunnel, then slide the trap into the tunnel. Place some fresh grass clippings in the hole behind the trap as bait. Cover the hole with a piece of plywood and place dirt around the plywood to seal out all light. The next morning remove the plywood and pull on the rope to remove the (hopefully dead) gopher.