This is a list of the best guard dog breeds. A guard dog is a dog that prevents someone from entering your property. The reason these breeds are the best guard dogs is mostly because they look intimidating and scary and have potential to do damage to someone (people are scared of them!). In all honesty, a dog that has not undergone months of guard dog training will rarely do any damage or overwhelm an intruder with force. He'll most probably just bark and get in the intruders way. However, most intruders will be scared-off if they know that you own one of these dogs (especially one of the breeds at the top of the list, such as a Rottweiler or Doberman Pinscher). These guard dogs do an excellent job of scaring intruders away!