Back to the original query.

What are you doing when he starts to bite? Are you playing, moving, sitting, standing, washing up?

If the dog does start biting what do you do? Say "NO!" and walk away, give the dog a command to follow such as sit, replace your hand with a chew he can have a go at?

If he bites when you are playing and the play gets a bit overboard and intense then he's worked up into a frenzy and needs to be taught to calm it by saying "NO!" and walking away over and over and over and over and over again until he gets the idea. Best way to do this is when you are playing with him, fetch would eb the best one with him being a retriever, is for you to
start and end the game.

I did this with Dillon by if he brought me a toy to throw for him in the lounge of in the garden I wouldn;t throw it straight away. I knew he wanted to play so I knew I had his attention. I placed the toy pruposefully on the floor and told him to leave, If he went near it then I used my foot or my hand to block his path as well as saying "AHA!" (my equivelant to CM's "Shhhh"). He would try and get to it initially and i had to push him back or walk him away and sit him down until he got the idea that if i put something ont he floor it was mine and no longer his. When he got to the point of bringing it, watching me put it on the floor and then backing away to lie down and watch what I did nextIi would make him wait for about 5mins before doing anything.
I would calmly pick the toy up and walk away from the area he brought it to and he would follow me. So if he brought it to me in the lounge I'd walk with it to the kitchen or the garden. I would then make him sit and only then would I play fetch with him.
When I'd had enough then i would tell him to drop it and then leave it. If he left it but when I started walking away i would tell him to leave it again and stand over it. Not as a dominance thing at all just if he went for it again I could block his path a lot more easily and give the command until he got the idea. Once he left it and walked away I would walk away too.
After five or ten minutes I would get up as though just leaving the room but go back to the toy and call him. We would play again and and run through the leave it routine until he got that play started and ended when I said so.

Soon after that the biting stop.