I agree with Spanielcrazy, if it even looks like your dog might take off you have to get after them and get them back straight away. I don't scruff mine and I don't tend to put them on lead, I would walk them back at heel, but either way is fine (lead or off, not scruffing). Ideally you don't give the dog the chance to bog off, you need to watch them like a hawk for the signs that they may be about to go so you can pre-empt it. If he starts looking too interested in heading in one direction you can stop whistle him and send him back in the opposite direction. Before I started hunting on even vaguely interesting ground I'd want to be absolutely certain of the dog's stop and turn whistle commands, these must be rock solid, you want to set them up for the best chance of success.
I agree with the 'hands in your pockets' thing. When the dog is hunting you don't want them to be looking at you, they need to be keeping an ear out for the whistle but ideally you want to interfere as little as possible and trust them to get on with their job so be unobtrusive and give as few commands as you can. At the beginning when I'm teaching a pup to quarter I use hand signals when I'm turning at the end of the beat (as I walk the pattern with the pup to begin with) but once they're past this stage I want the dog to look at the ground ahead, not at me. I hand signal if I need to send them out for something but otherwise I let them get on with hunting. You still need to give Benson the turn whistle and watch him for signs that he's going too far but that's really all you need to do, as he gets into it he should get into his natural hunting pattern.