Changing the Rules in the Hunting Field
The two major bad practices you see in the field are (a) never using a leash and (b) sending Pup to retrieve the bird while it's still falling.
Many hunters invest hundreds of hours in training their dogs, and then throw away the rules when they get in the field. They forget what a leash is for and let Pup indulge in whatever disobedience he fancies.
They spend hours training Pup to be steady. Then they get in the duck blind and start sending Pup to retrieve while the duck is still falling. After a few repetitions, Pup takes this practice to the next level. He goes without waiting to be sent. Next he progresses to bailing out of the blind at the gunshot.
It makes no difference how much pre-season training you do, when you get to the duck blind Pup is going to give you the amount of obedience and control that you require in that setting. If you want Pup to be under control in the duck blind, you have to tell him by demonstrating the limits of behavior.