If you are looking for a protection hound that is a different topic than seeing who does PP or patrol work with APBT's.. Care to elaborate your question? Fairly broad, there are a few members here including myself that own and work protection hounds that can answer questions but it helps if the question is a little more specific in what you are looking for.. Given that this is a Bulldog forum and not a Bandog, GSD, etc forum i can assume your asking about the use of Bulldogs vs anything else..
There are several members here that do Shutzhund with their hounds, which to clarify is NOT protection training in any shape or form.. This is a SPORT and majority of hounds that do this sport see it as a game vs work.. Meaning, chasing, grabbing, holding a sleeve is not the same as chasing, holding, grabbing a person. Of course, Shutzhund is a great way to test the character and overall mentality and physical ability of a dog, it is not the same as a real scenario where your life is on the line.. The stress and function a dog endures/needs to do either are not equal.
In terms of the dog itself, these hounds were not bred for protection or HA, rather for pit fighting.. So long as it scratched it was worthy of being called an American Pit Bull Terrier, otherwise all bulldogs or bandogs.. (Bandog in this context is NOT the same as Bandog Mastiff..) That said these dogs do excel in everything you can throw at them, world class workers that can do it all.. One thing that is always controversial is protection as these hounds were never meant for that type of work..
That said there have been a few HA dogs out there where the handlers kept and even bred these game dogs however the vast majority did not.. You hear about man biters, HA, etc popping up every now and then less than in the past in terms of game dogs.. More so than in the past due to piss poor "breeding" ethics.. These hounds could theoretically be used for guarding purposes however it is frowned upon by virtually all involved in the breed so its not really something discussed that frequently.. Generally only discussed in the form of debate between someone who agrees with the practice..
In terms of how to train, you are typically not going to get very involved answers on a public forum as in many places in the U.S, this is frowned upon almost as heavily as the act of dog fighting or []ing hog and dog together.. Also training, methods used, temperament testing, etc can all vary depending upon the program and how involved the handlers/owner of said program is.. Some believe just bite work with a sleeve is all it takes, some ensure their hounds can work under any real - life scenario and stress levels including firing guns, throwing objects, in cars, house break ins, etc..
It is important in terms of training to do a wide variety of scenarios outside the home.. Many dogs will naturally react in their "own" environment.. This does not make them protection dogs..
With any breeding program, if you are not breeding tested/proven stock you are not going to get to where you should be.. You cannot take just two dogs, breed them and expect a natural PP/Patrol hound that will excel.. Genetics genetics genetics! If your not breeding for the purpose than there is no purpose to begin with..
To keep this shorter and not go on and on about something you may not even care about, elaborate your question as to if you are looking at a Bulldog aspect of it or breeds designed for the task..