Hi
I'm glad you are looking for a new trainer. Mastiffs are a very sweet (and somethimes bull headed)breed, they don't take very well with this type of handling. What may work for one breed may do harm to the next. Your pup sounds like he may be teething, not showing aggression. Depending where you live, it may be hard to find someone who knows anything about mastiffs. Talk to your vet, talk to F.O.R.M. (it's a english mastiff rescue org.) they may be able to recommend someone to you. When we were (and still) training my boy (he just turned 2) we used positive reinforcement. I belong to another mastiff site and here is a snipet by someone who I feel is very knowlegable explaining it
"learning is a science. all dogs, eagles, people, lions, fish and turtles learn the same way, the brain chemicals are identical. i will add that each species also has hard-wired behaviors, described in "the misbehavior of organisms" that can sometimes not be overcome, even by the best and bob and keller and marion were the best (bob still is).
http://psychclassics.yorku.ca/Breland/misbehavior.htm (i would suggest that you do not attempt to say "the misbehavior of organisms" after you have had 2 glasses of wine because you will undoubtedly mispronounce the last word and be very embarassed....
eyeroll.)
there are rules of learning:
1. reinforce the behaviors you want
2. ignore the behaviors you don't want
these can be proven over and over and over and over and over, and have been in thousands, if not hundreds of thousands or millions of lab experiments.
behaviorial science is a science, held to the same standards as chemistry. published work must be reproducable, peer reviewed, challenged, re-proven, etc.
part of that science is learning how to learn. when we manipulate dogs into sit (pull up on collar, push down on butt), they are not learning how to learn or learning what sit really means, they are learning an avoidance behavior because they sit to avoid discomfort.
when we free-shape or lure them to sit, they are not only solidly learning how to sit, they are also improving their ability to learn.
dunbar tells a story about a seminar where the audience was dog trainers, with dogs. he asked them to stand up, face away from their dog and cue their dog to sit. these were experienced trainers, people who had multiple obedience titles. one dog sat. that dog was the only dog in the room who had been trained with a clicker, all the others had been trained to sit with the pull/push method. that dog absolutely understood what 'sit' meant. the others only knew it in avoidance context, not when their owners were facing away.
that's one key difference between positive training (which doesn't need a clicker but generally works better with a clicker) and the old pop and jerk training, the behavior is understood.
it's like tying shoelaces. no matter how much people describe it, you never really learn it until you do it yourself. dogs are no different, by figuring out how to do it themselves, they truely learn it. and they are making themselves smarter, they are learning how to learn so that everything they learn is learned faster and the behavior is stronger.
another thought are the studies done on children. asking a child to "climb down" is much more effective than yelling "DON"T CLIMB ON THE CHAIR".
since dogs and children have the same brain chemistry for learning, it's not implausible to consider that the same thing is true for dogs.
that's a brief snippet of the science side of learning. when it can be proven over and over and over that positive reinforcement works better than punishment, i'll take the proven method any time. "
Good luck with your new baby!