Ground hogs and rats, I use the same thing to stop them, used to have problems under the cement floor of the barn. I cannot remember the name, but I bought smoke bombs from our Rural King stores in this area, would imagine most farm stores either have them or can get them, might find them online. They look like a half stick of dynamite, and have fuses that you stick into the grey powder that is inside a cardboard tube. I light them, use the end of a shovel to push them down the hole, and cover the hole with dirt, leaving only a small opening so oxygen can get to the burning powder. I have never had a rat or groundhog come back to a hole I smoked out, although some may later make new holes, so you may have to repeat the process. I like the idea that there is no fire except the smouldering powder, so it is fairly safe to use under a building if the burrow does not open out into the building. You can see the smoke coming out the holes, sometimes it is surprising at all the exits you find by the smoke coming out of them.