While I'm not one for promotion of confrontation, you need to make it known, in no uncertain terms, that YOU are the GM, and that what you says goes.
A simple conversation before or after the game should, hopefully, get him on the same page. "Hey look, I know you have your interpretation of rules and what not, and please feel free to bring it up after the game, but while we're playing my ruling is my ruling and it's final until after the game. Period."