Though, for long term results, a cat is best. They are rightfully scared witless by a cat and won't come near the place. The cat hardly has to even work - just be there and look menacing.
btw, Glen, you beat me to a photo like that... 
P.S. Technically, a terrier will also work.
http://en.wikipedia.org/wiki/Rat_Terrier
Technically! The right Terrier and no critter in their right mind will venture within striking distance, it's in their blood to seek and distroy them. In some ways they are better than cats since they will dig out the burrows.
