I moved into a detatched inlaw apartment that had a rodent problem. After the second day of living there I saw a mouse and after further investigation found a lot of droppings in the attic.
I was in Home Dept. the next day and saw one of those "radio frequency" rodent and bug eliminators. Apparently it sends out some kind of high frequency radio frequency that effect them. I bought it based on the fact that I knew that I could return it at anytime.
Long story made short - 2.5 years later, not a mouse since. Added bonus - the main house (that I rent from) always has problems with black ants - not me!