guinea pig madness

hi i am gong to get  guinea peg for my b-day but i got andrew to think he's getting one and i don't want him to i just want it to be my guinea pig and my cage but if he did get one he wouldn't do anything with it i wouldn't let him eather because he is WAY TO ROUGH  so he doesn't deserve one i would have to do ALL the work he wouldn't do anything i don't know how to say ANDREW YOU'RE NOT GETTING ONE!!!!!! because my mom says that you got him to believe it but i don't know what to do!!!!!! HELP ME!!!!!!!!