After we rebuilt our Maine house and with the walls open it was pretty obvious when the mice moved right back in. Since all the doors and windows were new and tight I focused on the basement. I was pretty sure that they were getting in through small cracks around the basement door, around the basement windows and around the sill. I plugged all the holes with steel wool and foam and set half a dozen traps. For sure their numbers are down and we don't see them tip toeing around anymore but we do still see signs of them...if you know what I mean.
I'll add that someone told me to set up a 5 gal. bucket in the basement with about 4" of anti-freeze in it. The glycol is supposed to attract the mice (and the dog I'm afraid) and when they climb into the bucket they can't get out..... I haven't seen any mice in the bucket yet. Has anyone had luck with this idea?