Having an alarm system for your home is most reassuring, but a good old fashioned growling, barking .... maybe biting dog? might be an edge a homeowner would want to buy enough time to either bug out or arm and defend. What breeds and/or training do you think would be best and why? Personally, I would want a well-mannered but protective dog that is quiet until someone knocks on the door. One big enough to make an intruder second guess their decision! I like Labrador Retrievers, but mine would just wag their tale to any stranger....I would not want a real aggressive dog that would pose a biting risk to neighborhood kids and the mailman either....maybe a German Shepard?