We actually had an exterminator come by. We had to call them back after a month because they were still active all over the place. Seemed to work for a bit, but the next spring they had come back with a vengeance. I think we may have taken care of them some, but they had come from 2 neighbors still.
That spring, we found holes, put an empty mouse trap with a nail in the middle right at the entrance to the hole, then covered with a bucket. We started with five traps. 15 minutes later, I thought I heard a snap while in the house. We went and checked and had already killed 3. Dumped them and reset the traps. An hour later we had one in all 5 traps. Dumped them and reset all five again. Checked again in the morning and had 5 more. All told after 24 hours we had gotten about 20. That seemed to do it for the whole year. We were good for a few years, and got some last Spring, so we did it again. Got 8-12 that time, and haven't seen any sign of them since.
The biggest key is covering the trap with a bucket. I guess that makes them feel secure from hawks and stuff so they feel free to come out and play.