The biting stops when you tell him to stop so it's up to you.

Mine used to play bite when he got a bit carried away but I just stopped playing with him and walked off thus removing the reward. Biting = no play.

Play is the greatest reward you give a collie in my opinion. They live for it. Food treats work for about two minutes but they are too busy playing or wanting to play to be hungry sometimes.

How do you play with the dog is the first thing you need to evaluate. Is it tug-o-war games - a big no no. Is it hide and seek - a big yes yes.

If he starts to bite when you are petting him, rubbing his belly or playing then the easiest thing to do it just say "No!", get up and walk away. This ends the play session immediately. He won;t like it as he wants to play but he will soon work out why the play stopped if you are consistant and firm with your voice on the "No!" bit.

Don't set the dog up to fail so change how you play with him and what makes him reacts with a bite.

Good luck.