Why would you need to protection train your dog?
Either your dog is a good guard dog, or it's not IMO.
I have an excellent guard dog. He really looks like he would do something about someone coming onto our property. He goes berserk if someone hangs over the fence etc, snaps and snarls and jumps. However, if they were actually to get into the yard, the thing hed "do" would be lick and cuddle them. But he looks like he means business so it works as an excellent deterrant.
IMO, dog are either naturally like that, or they arent. You just mess with them if you are trying to teach them something that isnt natural for them.