The Three D's of Steadiness

Denials
A denial is denying the dog a retrieve.  Denials should be introduced early to the puppy.  Jack started denials about a week after he started retrieves.  As a rule of thumb, either you or another dog should pick up 50% of all bumpers/balls/birds thrown.  I will often take Jack in the back yard and have him sit next to me with a lead.  I will have my other dog Hazel come and sit on my other side with no lead (she is a bit more experienced).  I will then toss out a bumper or tennis ball and give each dog about 2 or 3 retrieves.  I will also toss out an extra 5 or 6 which I go and retrieve myself while the dogs stay put.

Delays
Ever since Jack started retrieves, I required a calm pup before I released him.  At first I just waited for the first sign of calmness before I would just let him go, calling his name is a release indicator.  Gradually as he has gotten more steady, I have lengthened the time he has to wait in order to earn the retrieve.  I will often line up to his right and mark the bumper with my pointing hand.  I then call his name and release him for the retrieve.  Dogs should never go after a retrieve unless instructed to do so.

Diversions
Diversions are a bit more difficult and I have not yet incorporated them fully while training with Jack.  I have introduced diversions to my dog Hazel and she seems to handle them well.  Diversions are bumpers/balls/birds thrown to distract the dog while an action is being performed.  For now, I place both Jack and Hazel in a sit position about 10 yards apart.  I then throw a tennis ball right between them.  They are expected to stay sitting and not go after the ball (this works most of the time).  With Hazel, as she is bringing back a tennis ball, I'll throw another tennis ball over her head, directly in front of her, to either side, or behind me.  She is supposed to stay focused on the current retrieve and bring the first ball to me before I release her for another retrieve.  Sometimes she gets released to another retrieve, other times I use the diversions as denials and go and get them myself.