German Shepherds, in our opinion, top the list of best family guard dogs due to their natural instincts to listen, learn, and obey. (caninejournal.com)
I have them listed as one of the best family guard dogs because of those reasons you put down in your comment! (pethelpful.com)
This breed is also larger and considerably stronger than the other members of the terrier family, making this an ideal choice for family guard dog. (animals.howstuffworks.com)