Rohan is 13 weeks tomorrow and a lab.

His biting/mouthing has gotten much better and is soley directed at myself and my husband. Everyone else just receives licks!
However when he is excited, or in 'the zone ' as we call it, No amount of walking away, saying no, or toy replacement works. he just wants to bite our hands!
We tried putting him out/behind baby gates etc but he just starts chewing whatever he can find in the area we have put him in.

He had his first puppy training class last week and a couple of the other puppies tried to bite the instructer. She gave them a short/sharp yank on their collar.
We tried this at home by putting Rohan's collar on when the behaviour started and it seems to do the trick, the collar alone seems to switch his mind onto something else. If he bites we give a quick pull on the collar and get him to sit. It's not 100% effective but it is definitely the best method we have found. His collar is just a standard buckle one. (definitely not a choke chain or the such), the movement just distracts him rather than hurting him in anyway.
Sorry for the length of the post but I know how frustrating it is when nothing seems to work and boy are those little teeth sharp!