One advantage breeders have is the opportunity to observe how a bitch behaves with her pups. I've been lucky enough to have a window into this behaviour because one of my friends is a breeder of Great Pyrenees.
We can learn a lot from observation. Case in point, when puppies get close to weaning age, the bitch gets tired of feeding them and will cut feeding sessions short by getting up and walking away. She exhibits the same behaviour when playing with her offspring when she tires of it or if they become too aggressive. As a result, pups understand from infancy that walking away signals end of food and/or play. We can use this knowledge with our young dogs when their play is aggressive. Walking away is a signal that playtime is over, and once it becomes associated with specific behaviour, e.g. biting and playing rough, they learn that fun time will cease when they display this behaviour.
You may have observed dogs playing at a dog park. If a pair is playing and one has had enough, again, the usual disengagement is to walk away. If the other persists, sometimes it leads to a nasty encounter, but usually a brief growling and stiff legged departure ends it.
So what do we do if the pup doesn't take the hint and continues to persist by following and nipping? What does the bitch do? If ignoring him doesn't work, she often snarls in his face, and/or pins him down with a foreleg. My own approach (which has always worked for me, your mileage may differ) is to restrain the pup, who will initially struggle or try to bite, but I don't release until he is quiet. Then "good" and let him go. Rinse, repeat.
I learned a lot from my breeder friend. When dealing with a large breed you cannot afford to let bad manners go in your pup, who when mature is likely to outweigh you!
For anyone wondering where walking away lands in "operant" terms, I would label it negative punishment, i.e. removing something the dog wants (your attention) to cause the undesired behaviour (biting) to cease.