Devils advocate here - shouldn't the bond be built between the owner and the dog, not broken down to be built by a stranger and then again by the owner? The prong collar bothers me as well. Why does he need to use a tool?
I can completely understand your concerns - but I've trained with prong collars (so have many other people on this forum) and have had great success with them. I can't stress enough how great of a tool they can be, especially for hard headed dogs. Although I respect your opinion on the prong collar, its
not a negative tool. There are some dogs where it's necessary to use a tool, if for nothing else, to help the process move faster and to gain more consistent commands. Prong collar training is a very calm type of training. There's no yelling, there's no rough-ness with the dog, it's simply an easier (and more down to basics) way to let the dog know what you're asking - while giving you a way to let them know you expect them to do that without question. It accomplishes the same thing a momma dog would if their pup acted up.
Also, with very strong dogs that
do have behavioral issues - it is a consistent method, very repetitive. Sit, down, stay - over and over. If the dog doesn't respond (as stubborn dogs will ignore) a slight correction is given. Why wouldn't you use that tool? Especially if it's between you worrying about your dog biting someone, and using a prong collar to give corrections. I'm going with prong collar, and I've seen the results and work with them regularly.
The bond is always with the owner - training, or correcting bad behaviors is a great job for a professional. Especially someone that has experience working with these types of breeds and will work for an extended amount of time with the owner on training after the initial training session is done.
My trainer also rehabilitates rescue dogs for shelters. He does this all the time and recently was shown on Animal Planet helping to train therapy dogs. He offers a boot camp that sounds very similar. The dog goes to boot camp for two weeks, after about a week the owner can visit. It's all prong collar training and the results are wonderful. So many owners (even friends of mine) have done it with dogs they had issues with and they came back trained. So did the owners.
I think this is a great thing for Franklin and he may be confused at first, but in a different environment the trainer will have a chance to work with him, instead of fighting for his attention over guarding the owner and the house.
Training separately from the owner doesn't do anything negative to the bond with the owner at all - in fact, once the owner learns a few things as well it will
greatly strengthen the bond between dog and owner.