Hi shurweee,
I don't have the solution to the biting problem, but I don't think you should hold him down on his back. That's called the "alpha roll" method. It is no longer recommended to do it, as it's basically saying "I'm gonna kill you". The only reason a dog will forcefully flip another dog over on its back is to kill the animal. You can look for "alpha roll" on the internet if you'd like to read more about it.
http://dogs.about.com/cs/basictraining/a/alpha_roll.htm By forcing an animal to submit in that way you are literally putting the fear of death into them, they think you are trying to kill them. ...Doing this behavior to an already dominant animal can increase the likelihood of aggression. Doing this to an already submissive animal will increase the fear in that animal