Will My Pit Bull Become Less Protective?

Nothing territorial will change. Its just in a dogs nature to be watchful of their territory. But don't make the jump to think he would protect you, neutered or not. APBTs love people, for one, and you should not depend on a dog who isnt trained and bred for real protection work. Get a gun if you don't feel safe; though I don't most people would cross your pitbull anyhow, he will be a good enough deterrant.