mad mad

caught 2 in the back yard last week-they have a den under the wifes art/craft building in the backyard. Been fighting them for 3 years now since we moved in. What is the best way to irradicate them completly? Sure don't want to tear the building down, but it might be coming to that. was hoping our dogs presence would be a deterrant, but not so much. trying moth balls in the hole they crawl under the fence and in the holes they crawl under the building, set that up this week-also plugged up the holes were they crawl under the fence-anything else we can do?