When I was buying Remy's first prong collar, (for after a 2 week training/trainer absolute fail that I take partial blame for, for being dumb enough to think a 2 week board and train would get her to listen to me, when really, I needed help LEARNING how to train her, myself), the cashier commented on how they REFUSE to train dogs that have been previously or are trained with prong collars. I decided then, that if I ever needed another training program, I would NOT be going to them.
Yeah the reason why they don't allow ANY form of corrections is that they have managed to "produce" training like a product. And as a large franchise it'd be a huge liability and risk to allow any form of corrections or prong collars. Not that it's not useful but from a business standpoint, it only takes a few trainers that mess up to get a big lawsuit whereas with positive training, less can go wrong in the eyes of the public.
My dog may need to get on the prong or some training collar soon. She doesn't even respond to martingale corrections whatsoever. She will sit and make eye contact when I stop but the minute I move my feet she darts forward with all her force. I tried stopping and starting again, over and over and over but she will just stop, relax and when it's go time she will sprint with full force. I do like Michael Ellis' approach to leash pressure, which is very simple really. You put on a training prong collar, and you give SLIGHT, constant pressure. So if the dog is next to you, you pull forward on the leash (straight forward, not up) and the dog will give into the pressure and the minute he/she does, you release pressure, mark the behavior with "Yes!" and follow up with a treat. Pretty soon he or she realizes that to turn off the pressure, just to move away from it quickly and there is negative reinforcement (take away the bad feeling from the leash) as well as positive reinforcement.
He also mentioned that dogs that get only positive reinforcement (he had 2 dogs like this) have problems later, and both his dogs shut down for his protection work and what not because they never learned how to deal with turning off pressure or stress. I think that's a very good trait to have in a dog that ultimately helps them to cope with stressful situations and to become a more hardy dog. but that's kind of off topic.