If it is legal in your state, a hand full of moth balls down the hole, then get ready to start blasting.
Some years ago, I ran into an old coot that was setting gopher traps out on a huge field of ground squirrels, a little red flag would go up when the trap had caught one. Bounty on the gophers was $1 each. The old boy ran out of traps to set, and he was pulling a pretty good size propane tank behind his 4 wheeler. I thought to myself that the old coot had converted his 4 wheeler to run off of propane.
I complimented the old coot on his propane conversion on the 4 Wheeler and he just started dying laughing. He told me to follow him. We found an active gopher hole, he pumped the gopher hole full of propane, and he had an igniter attached to a cord. We backed off a ways, then he ignited the propane, the ground blew up! This was back in the 80's, probably illegal now.