It's such a shame that the outdated Alpha Roll is still used by some people as a training method. It can make an aggressive dog even worse and is very dangerous:
Alpha rolling is dangerous and unnecessary. By performing what seems like an attack to a dog, humans leave themselves vulnerable to a bite to the face and lower the trust and respect their dogs have for them. An alpha roll can have dire consequences for dominant or fear aggressive canines. An alpha roll can increase aggression in an already dominant dog. In a submissive dog, the alpha roll will add more feat to the dog's psyche and can lead to submissive urination, loss of trust and possible fear biting. The alpha roll is not a good way to build a sound, healthy relationship. A stable leader shows his dog the rules in a fair, gentle, and firm manner, built on clear communications and mutual respect.
In the dog world, the only reason one dog will forcefully flip another dog on its back is to kill it. http://dogs.lovetoknow.com/wiki/The_Alpha_Roll