If you're a game developer, what would you use to combat used game sales?

[FullMetalMerc]

I think each game disc should have a one time code for online play limited to either one console or one account or gamer tag. if the person sells the game and some one else buys it their should be an option in the games menu to "re-register" the game which would cost the player something like $2-$5 so the developer would make money on the used games sales if ppl wanted to play online. This would make lots of money wit games like COD and Halo ,IMO.