I found a couple of things:

1. http://www.thriftyfun.com/tf634141.tip.html

Peppermint oil works! My wife did it last night after we found out we had mice in the wall. The traps that we put down had no affect after a few days, so we dropped a bunch of peppermint oil soaked cotton balls in the wall and closed off the holes with a garbage bag. I just wanted to see if they would come back in. And this morning no holes in the bag. However the dogs wanted to go out at about 4 in the morning and in about 5 minutes they had mickey and his friends cornered. Too bad they couldn't finish the job. Their snouts are too big to get under the smoker. So, either get peppermint oil or get a rat terrier.
2. http://www.care2.com/greenliving/sca...naturally.html

3. http://www.ehow.com/how_5367093_make...repellent.html