People overestimate their dog's ability to recognize and engage a threat. Example: The murder of Sarah Stern. Her schoolmate, Liam McAtasney, planned to murder her and rob her house of a bunch of cash he thought she had. He drove around with her (they were sort of friends) and did errands, and then took her back to her house. Nobody was home except for her big German Shepherd. When they went inside, Liam waited for Sarah to have her back turned, and launched his attack. He grabbed her from behind and began strangling her. So, of course, during the ferocious physical struggle which ensued, the German Shepherd jumped into the fray and tried to protect his owner? Nope- Liam said that he was concerned about the dog, but when he was killing Sarah (which took about 45 minutes), he said the dog just cowered in the corner. Sarah even called the dog's name a few times, desperate for help, but to no avail. Liam choked her out, plopped her onto the bed, and then continued strangling her. She wouldn't die, though. He's a bit of a bitch, physically weak- he ended up stuffing a shirt down her throat and smothering her to death. Over the course of 45 minutes. Dog didn't do a damned thing. All this being said, here's the role that dogs have historically always been great at- **THEY ARE A FANTASTIC ALARM SYSTEM FOR INTRUDERS.** Any breed, almost any dog will start making a racket if they hear/smell someone slinking around your yard or messing with a window. **Their purpose as protectors is more about ALERTING THE OBLIVOUS HUMANS to the potential danger, so that we can grab a weapon or form a plan to deal with the threat.** And there are some dogs that will intervene in a fight, but more often than not, they sort of just run around, watching their owner being stabbed or beaten to death.