just because it is an accepted method doesn't mean that it's a good idea.
Alpha roll theory is very simple to debunk.
1) your pup knows you aren't another dog.
2) alpha rolls in the canine world are VOLUNTARY behaviors on the part of the submissive dog.
3) if the dog is not submissive to you, you are going to have a fight on your hand that you will LOSE because even a young pup has teeth and can do a number on your face if he decides to fight back.
So, any dog that you CAN roll and discipline this way doesn't need it. Any dog that is truly dominant is going to fight for the alpha position and not submit calmly.
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I had the opportunity to meet a trainer early in my career who still had the scars on his face from an alpha roll gone wrong. He admitted in hindsight, he should not have attempted to roll this dog and put himself and the owners at risk. When you put a dog in a defensive position, they will try to fight you; its natural. In most cases, people receive multiple bites to the forearms upon releasing the dog and in some cases, the dog will get the chance to inflict a damaging bite to the face.
I try to explain to people that first; your dog should not fear you! Wrestling your dog to the ground and trying to overpower them is pointless and causes more damage psychologically. You simply cannot win a fight with a dog without getting hurt. A dog generally will not take on a challenge they cannot win and people should learn this too. Even the smallest dog can inflict damaging results with their teeth. Secondly, if you have to keep correcting, youre obviously doing something wrong!
http://tarastermer.wordpress.com/2009/01/21/why-you-should-not-alpha-roll-your-dog/
Even the Monks of New Skete who made the alpha roll so popular now admit that it was never a good idea.
http://www.4pawsu.com/DebunkingDomMyth.pdf
"Take alpha rolls. The early researchers thought that the higher-ranking wolf forcibly rolled
subordinate wolves to exert his dominance. Modern studies have shown that alpha rolls are part
of an appeasement ritual offered voluntarily by the subordinate wolf, not forced by the superior.
A subordinate wolf offers his muzzle, and when the higher-ranking wolf pins it, the
subordinate rolls over and presents his belly. There is no force. Canine behaviorist Jean
Donaldson, author of the award-winning book
The Culture Clash, says, The truth is, there is not
one documented case of a wolf forcefully rolling another wolf to the ground. Nor is there one
case of a mother wolf (or dog) scruff-shaking her puppies.
A wolf would flip another wolf against its will only if he were planning to kill it. The same goes
for a mother shaking her pup by the scruff. Both are rare events."
An over the top example, but this is how an alpha roll looks to your dog: