What is a "guard dog"?

This question has many different answer dependent on the persons observation and experiences. Most people (meaning dogmen) feel that a APBT is the farthest from a guard dog as you can get. But it really depends on what you want out of your dog. Rott Weilers are said to be great guard dogs, but to me they aren't. Put your self in the place of a business owner. Would you want to come to work one morning and find a body or two laying on the floor? Not to nice huh? A large percent of Rott Weilers are phony, they bark and put on a show as if they want to really want to bite. But they really just wanna scare it off. ARott is a dog that will only attack if attack trained or feels that his life is endanger, but there always the exceptions. But they make good guard dogs because of there size. If you take a average APBT and threaten its owner there is no doubt that it will hurt that person. But some other breeds just bark and growl. The only reason I feel that APBT dont make good guard dogs is that they dont see all people as enemies and could be easily tricked into trusting a person. There are and will be always exceptions, and once you understand dogs you will be able to get what you want out of your dog.