I have pulled together a list of three books that have scary dogs (or werewolves - which in my opinion, are still dogs since they are in the canine family).
The first book in this list has to be Cujo by Stephen King. That rabid monster is probably the scariest thing I have ever read. King brings the mental breakdown of a dog to life and the fight between human and nature becomes all too real. You will avoid dogs after reading this one.