I would suggest that if you are going to "alpha roll" a GSD then either he/she should be very young and small OR you had better be very physically strong enough and know what you are doing as it could get very tense very quickly depending on the dog and his/her personality and your relationship with them.
on the other hand, i have had to get physical with my dogs on a couple of occasions (back when I was younger and more brave (foolish). Once when my then 10/11 mo male GSD (from one of the toughest male GSD German imports decided that he didn't want to give up his real bone that I had given him and showed his teeth and made a really nasty growl when I reached for it. Without thinking of the consequences, I grabbed him by the scruff of the neck and gave him a very low "NO" and a shake. He accepted it and never again decided that I could not take something out of his mouth. Second time was when I threw a toy for my two female GSD's to chase and the younger one got it first and the older decided that she wanted it and jumped on the younger one and it was on! I grabbed both by the scruff of their respective necks and told them to stop it and by some miracle I was unscathed - could have gotten bit by both of them I realized later but it turned out ok. I was lucky!
But I often wonder what would have happened if i had backed off from my young male GSD when he growled??
on the other hand, i have had to get physical with my dogs on a couple of occasions (back when I was younger and more brave (foolish). Once when my then 10/11 mo male GSD (from one of the toughest male GSD German imports decided that he didn't want to give up his real bone that I had given him and showed his teeth and made a really nasty growl when I reached for it. Without thinking of the consequences, I grabbed him by the scruff of the neck and gave him a very low "NO" and a shake. He accepted it and never again decided that I could not take something out of his mouth. Second time was when I threw a toy for my two female GSD's to chase and the younger one got it first and the older decided that she wanted it and jumped on the younger one and it was on! I grabbed both by the scruff of their respective necks and told them to stop it and by some miracle I was unscathed - could have gotten bit by both of them I realized later but it turned out ok. I was lucky!
But I often wonder what would have happened if i had backed off from my young male GSD when he growled??