And another simple trick for keeping rats and other rodents away - go to your local wildlife park and ask if they sell bags of snake poo. Sprinkle a bit of that around and rodents will disappear for about 3 months. It doesn't hurt to throw a few chunks up in to your ceiling cavity either.
I have done something similar, using wolf urine to keep deer away from gardens. It's just very stressing to collect the urine. Sneaking up on the wolf at the right moment and positioning yourself just right with a bucket is not an easy task and wolves don't like it.