i say keep your oscar. they are so personable and cute, who cares if they like to rearrange the tank to their liking?
my O is constantly doing stuff in his tank that ticks me off, but it's all part of his charm! i've made the tank bare bottom so that he can't push substrate into piles or make sand blow all over the place (and into the filters!). his decor is a plastic resin 'wood' piece from petsmart with a plastic plant entwined in it. (see my avatar - the lower piece of 'wood' on the right has been removed, so just the tall one remains, and the sand is gone now). my O also constantly knocks the rena filter intake into the water, but i don't mind, it entertains him, and the top fixed part of the intake is always underwater so i never worry about the canister running dry.
i give my O a floating orange plastic ball to play with and chase now and then, and he LOVES to hunt the laser pointer that i shine into his tank sometimes. he will let me touch him lightly on the side, almost like a petting, and i swear he hears me from across the room when i tell him to knock off whatever he's doing bad and behave himself!
gee, can you tell i'm a devoted oscar momma? lol!