I had rats move in once and they say, "If you see one, you probably have
hundreds." I got rid of them all in one day by setting out bowls of dried
squash next to bowls of water - I'm told that instant mashed potatoes works
well too.
I've been mixing plaster with finely ground corn meal and make it
available free choice in small dishes. It seems easier than making
peanut butter balls. Their gastric juices do the rest.