Imagine if they started training pup with obedience and very few retrieved marks at home. Marks are a very small part of the 'Balanced' or 'Total' retriever if you will. Many marks can be thrown with very few retrieves in order to teach patience and obedience.
On days that they came to 'school'......more obedience around truck, around other trucks and people. NO CANDY, or I mean MARKS. This sort of 'off site training' goes on several times before an actual MARK is ever thrown for the pup until it is calm and controllable around others.
Walk pup to the line several times just to watch others calmly, so it learns that each trip to line does not get CANDY. Only when pup can sit and watch mark thrown calmly and quietly does it actually get to retrieve.
For dogs who are already out of control going to line and on the line, this will also work wonders. Back to basics to regain control. Dog must learn that they are not in control. Only when they have complied with master's wishes does he get CANDY!