Which dog breeds are violent?

[Eddy Dumire]

I'm considering allowing dogs and cats in my newest listing and need a little guidance from the community.  I've never really owned a dog, though I have had cats.  We just put brand new carpet in the house in addition to repainting.  We're still on the fence about refinishing the floors.  If I want to control some of the potential damage, which dogs should I refrain from renting to?  When people have asked, I've generally said no very large breeds and no violent breeds.  A guy just called and asked about a german shepherd.  I know they can be trained to attack, but does the by definition make them a violent breed?  A Chihuahua could be trained to attack too.