One of the most protective dog breeds is a Tibetan Mastiff. This breed is famous for not liking anyone else except his family. Originally kept inside during the day and then turned out at night, they are quite well-mannered inside, though extremely independent and not to be trusted off leash outside unless confined (www.akc.org).
The Caucasian Mountain Dog was developed in medieval Russia for guarding livestock. It is a powerful, robust breed, popular at Russian dog shows. Its temperament remains cautious with strangers & difficult to obedience train. It is not recommended with children nor other dogs, nor in urban spaces. The thick, dense coat provides good protection against cold weather.