I disagree...a properly trained dog in Sch, ring or PSA is far more reliable than just trusting your dog to keep you safe...and if you do give such command you need to out the dog on command. You know a properly trained dog has the nerves will, desire, strength to fend of the attacker and it is bred into them by proven parents and grandparents. A pet, yes they have breed descriptions and may bark and look serious but you dont have a clue if they would deliver if need be
Training dogs in such a manner improves a handler and dog bond, people do it because they truly love training their dogs more so than a dog to 'protect' them but relying on a unproven dog to protect you is a rather large gamble. It is more than just biting a sleeve, it is the MAJOR OB, teaching a dog to track, long sends and downs etc...
Say someone goes to harm you and your dog latches on and is really pissed off, how the h*ll are you going to out a 200lb pissed off animal...can you tottaly handle a 200+ pissed off animal...you need to have absolute control of that dog and the dog needs to trust you 110%
A PSA, SCH are trained to take different sorts of pressure in different areas and chances are if a person shoots a gun your dog is going to run the other way because it is natural 'flight' response or they kick your dog, they dog may give up and once that happens you could break your dogs confidence.
Trained dogs need to be stable dogs, they have to be able to working within large groups of people and act like they dont exist...if they have too high of a civil aggression they arent going to do well on the streets hating the world around them. There are some that are even therapy dogs along with being titled SchIII or PSA dogs
and for a visual...here is a 185lb male CO out of Caucasian Legend a breeder that I have a pup from.  He isnt very happy at the moment because he is being evaluated in temp by a professional decoy and has had no formal training...Yel
ana has complete control over her dog and the second she tells her enough, he sits right at her feet as if nothing ever happened. Balou hasnt taken a bite yet because he is not yet ready to go that far.
But a good visual on an angry BPO and a reminder to what an agry large dog looks like