@Rumpelteazer --- I don't know if it is an option for you, but this is something that worked for me --- I happened to have a rodent problem. I then happened to be keeping a friend's cat for one weekend. At the end of the weekend, I had no more problem. I think just the *smell* of that cat frightened them away.
BTW -- I tried the "supersonic noise" device, but several Japanese friends told me that was like a "jukebox for mice", and they just dance to the music
