Sorry, I gotta disagree here. Most dogs will not back up a growl, and if they do bite, it's a fear bite. A fear bite is done to try and get whoever/whatever is bothering the dog to go away. The dog does not want to engage in a fight, they simply want the problem to cease. They posture and growl, and then maybe take a cheap bite as a last resort. In reality, a lot of dogs that are protective breeds will do the same thing. In just the last 4 months at our dog club I've seen a half dozen GSDs, Rottie mixes, big American Bull Terriers who wanted to join us, and none of them would engage a person who was making threats towards them or their owners. Most showed total avoidance. The rottie mix even laid down as a simulated attack on his owner took place. ALL of these people thought their dog would protect them, and none did or showed any desire to. Imagine the lady who was having a simulated attack done on her and she's watching her trusted protective pet lay down and not even pay attention to her screaming. She got a dose of reality real fast.
Put one of the dogs you were talking about- cockers, chis, crested, whatever, up against someone like me. Let it growl and posture and I'll make one assertive, quick, menacing move to that dog and it will most likely pee itself. It's not going to attack me. And if it does, it gets punted, and I guarantee it isn't coming back for more. This is what someone who is determined to get you or your property is going to do, a little dog is one small obstacle in their quest. In turn, show me a GSD, a Rottie, Dobie, Bouvier, Mal, that is silent and is standing it's ground with confidence, I'm not going to test that dog. That's the dog that will have no problem taking the fight to you and who won't give up.
I'm not sure what to tell the original poster. A dog that will really protect you is not a dime a dozen dog, it has to have the right genetics, the right training, and is going to be a LOT of work. For a dog like that 99% of it's life is training, and maybe once does it get to prove it can do what it was trained to do. There is really no way around it. Maybe getting a giant dog like a Mastiff is best because they are a great deterrant, but they still require a lot of training and won't be mature enough to really do anything protection wise till they are at least 2 years old.
The main point of my post was to try and quell this myth that any dog will protect, it's simply not true.