How do i prevent my brother from playing my xbox live arcade games. ?

Alright. Well I got a 4000 microsoft points card and bought tons of xbl arcade and indie games. When I came back from work he had been playing them with his account. He has his own games and he doesn't like me playing them but he plays all my games all the time (black ops, mw2, red dead, bbc2, he actually destroyed my transformers wfc disc, and now all my arcade games. Normally I just hide the discs when I go to work for nine hours. But I can't do that with the xbl arcade games. So what should I do. Should I move them all onto a flash drive and run the games from the flash drive or is there a setting to prevent access to other accounts on the same xbox. And if I did the flash drive thing would it slow down my process of the games like Fortress craft or something