I used to rent a barn with a friend to use as a workshop. It was right next to a big grain store and the rats there were the size of cats. They did used to have the rat-catcher come around with a gun and two jack russels and he kept the numbers down but at one point we had a problem with them in the shop, they were coming up through some holes around the edge of the slab. In order to get rid of them we decided to gas them, plugged as many holes as we could fine with rags and bits of wood and then wedged a hose up the tailpipe of a car, shoved the other end down a hole and left it running for a couple of hours. Seemed to do the trick, there was certainly fumes coming out of the floor all over!
Now I have a problem under the tin barn I rebuilt half of last year and legally I can't do anything about it. It seems we have a Badgers sett under it, there were some holes there when we moved in but they clearly weren't in use, anyway, a month or so ago suddenly they came back and have dug right under the slab, theres two big piles of dirt a good two foot tall and two large tunnels. Trouble is they are protected by law. I like badgers but don't really want them undermining my shed, its also going to be a problem as we want to rebuild it from scratch in a couple of years time as we only managed to save half of it after one end collapsed. The burrows are in the middle half open bit and go under the slab on the left.