I dont see any problem with putting a lead on a dog and hanging it over, say, a thumb hole stick which weve pushed into the ground on reaching our peg.
Done this way there should be no need for a corkscrew but, what the heck, if using one gives you peace of mind, go for it!
Ideally we should all own dogs that sit quietly at the peg and only move when told to as you say, its the sign of a well trained gundog.
That would happen in an ideal world but we dont shoot in one, do we?
For all sorts of reasons even some of the best trained dogs develop bad habits which their owners havent got the time, or experience, to put right.
Granted, it doesnt always look good to see a dog tied down in this way but I would far rather see it restrained and sitting quietly at the peg than careering around the place after every bird that drops.
Tethering in this way means the owner can let it off after a drive to retrieve a bird or two as a reward for sitting quietly.
Lets not forget, either, that a days driven shooting isnt cheap and to have an unruly dog running wild is a surefire way of ruining your day: its impossible to keep one eye on the dog as well as trying to concentrate on your shooting, especially when the drive gets a little bit busy.
Regardless of what some people might do to keep their dog under control I would always recommend that they sit the dog 4 or 5 feet in front of them at the peg so that they can instantly spot any movement and correct it.