I have done (and will do) just about anything to break up a dog fight. I'm not remotely proud of it, but I'd rather have an injured dog than a dead dog.
I have never smacked one of my dogs when we're training. I have pulled on the leash, not hard, it's usually a quick frustration tug and it's always a sign to me that I need to stop and take a break before we keep moving. I did use leash pops and corrections years ago with my sister's dog when trying to work on LLW. It didn't work and I'm not proud of it. Oh, and Murphy had a prong collar for about six months shortly after I got him. I've poked Mu (in the haunches lol) to get her attention before - especially in situations where we can't just back up to get her under threshold.
I dunno. I can't imagine smacking/beating/kicking a dog to get what I want, not with the knowledge I have now. My Dad was a very traditional trainer with our first family dog - she'd get into things, look "guilty", he'd beat her, and the next time she was left out with food, she'd eat it. Now when he leaves food out my mom tears HIM a new one because Max gets into it. It's hard to blame a dog for something that's actually your fault.