You buy those metal traps, and anchor them with some wire to the surface of the ground, then you find a place about 1 foot down the tunnel and place the trap under the sod. The reason you have to anchor it and put it down the tunnel a ways is because if the trap doesn't kill them instantly, they will carry the trap with them deep down the hole. If you try putting the trap at the entrance of the tunnel, they will see that you messed with their dirt and they will just push more dirt up in there and set off the trap early.

I caught about 10 of them one year.