I would suggest any of the healer breeds. I have a pure-bred red healer from austrailia and she is VERY territorial. If someone comes near a car she is in (even if she knows them) she will go ape-shit. Talk about loud too, they will wake you from a dead sleep. They are very well mannered and train easily. Any out-of-place noise outside the house at night and she goes off. She is a mid-sized dog and has pretty good muscle size.
She has had no professional training, and she responds to just about any command you tell her. We have her trained with whistles, since she works with the cattle a lot. Even if someone she knows tries to come up to her and pet her, if I tell her "Don't like" she will nip at them when they come up. Very well behaved dog when you want her to be, but extrememly mean if she feels threatened or doesn't like your vibes.
Any of the healers are pretty expensive around here since they are very good cattle dogs. $1500 is a good price for a pure-bred healer around cattle country.