Howe do I train a Shar Pei/German Shepherd Cross as a good watchdog or guard dog?

A shar-pei is very protective of his territory. My grandma has one & will not let no one in the house. He barks at the window if he hears anyone outside or hears a car. She had a cop come over one day & he bit the cop! They tend to get close with the owner & theregore feel it's the duty to protect...also known as the chinese fighting dog. Very smart & intelligent. I had a german shepard when I was a kid & we still have one of her off-spring which he is now 6 years old & one of the meanest dogs in our town & we've had animal control after him for years. Both breeds get protective of their territory & owners. It's not really about training them, it has to do with age. The less people you familarize them with it'll start the natural instincts to protect. You have to show them which people are oksy & which ones to be aware of. If your walking it then keep him close to your side & keep interference with others kept to a minimum.