Ditto to LEO’s post. At one time I raised and trained German Sheppard’s for protection dogs. We sold to many of the Southern Cities back in the late 50s, early 60s. At the time a “protection dog” was mostly an attack dog that would attack anything but it’s trainer/handler. Some are still trained this way today, but most are trained to attack on command only. That said, the nature of a dog is to protect it’s territory, most all breeds are territorial to some degree, some more so than others. Having worked dogs, I can truly say a dog can not match man intent to overpower or take it out. I am meaner than any dog I have ever met, maybe not with bare hands but then a thief would not normally approach a place without some means of protecting themselves. A dog is a very effective “early warning system,” all they have to do is bark I have three that lets me know if someone is near the house, they supplement my ADT system.
My son and his wife had their house broken in one night, they lay in bed while the robber was in the room with them, and he took $1200. out of my son’s wallet, cash and jewelry from a dressing table on the opposite side of the bed, neither of them ever woke up, they had three dogs. My daughter-in-law had “beaten” the dogs every time they barked prior to this so they never even whimpered while the intruder as there. Today they have a new Dog, a 3-4 pound Pomeranian but it barks at every movement around the house, doing what he is paid to do.
Bottom line, I wouldn’t count on a dog alone for protection, as a warning system great, and if they will bite that’s a bonus, but keep in mind most any man can eliminated the dog if that’s all the protection you have. And a male dog can always be led off with female "in season."