Answer:
When trying to determine which breeds are best for guard duties there are certain criteria that you need to look at, such as protective instinct, mental soundness, Intelligence, nerve, obedience, ability to take, and athleticism. First off lets start with protective instinct, because if the dog is not protective by nature then he will be much less affective than one who is naturally a protector (In my opinion the most important). Mental soundness means the dog is stable in attitude and judgment, so the dog can make sound judgments and act independently. Nerve is the ability to stay confident in an adverse situation and not to be timid nor shy, because when a situation arises it may not be in a ideal or friendly surroundings (Also dogs that are fearful will bite and be overly aggressive.). Obedience is not to be overlooked because with a dog trained in this manner you must have authority and control at all times (If not it will be a danger to you and any one else around .). Ability to take is when it is asked to protect it will not release nor back down when counter attacked by the assailant, also it refers to the dogs ability to recover. Athleticism is pretty much summed up by the ability to run down and subdue the assailant, because if the dog is not fast enough to catch the person or strong enough to hold them then all is for not. There are many breeds that have the attributes that are needed, but the main breeds mentioned from what I have read are rottweilers, German Shepards, dobermans, bull mastiffs and Pittbulls. In my opinion bull mastiffs have some attributes but fall short in others, because they fall way short in intelligence and are to bulky to be as athletic as the other breeds. Pitbulls were bred as fighting dogs not as true working guard dogs and fall short of the natural protective instincts of the others. Dobermans are a better fit than the other two but in my opinion it does not have the rock solid nerve of the German Shepard nor the rottweiler and lacks the strength of the Rottweiler. German shepards have all the attributes except size and power when compared to the rottweiler. In closing I believe the rottweiler is the perfect blend of the criteria to be the ultimate guard dog.