Dang.  Ratzilla?

For something that big, yeah, get a 15-20lb cat(Siberian Forest or Norwegian Forest cat or similar) or a Terrier.  No 3-4 lb toy cats need apply.(though most any cat will still scare things like pack rats away because they don't want a fight)

I mentioned the Rat Tarrier because they aren't cats - lol - and some people don't like cats(dunno why, but there are non cat options as well if you want a dog).