You could always go to a local home depot or what ever it is in your area and see if they carry "security screws" Its a weird looking screw with just two holes in it. It takes a special bit to be able to put them in and remove them. Then its just a matter of replacing the four screws that hold the radio to the bracket and the other four screws the hold the bracket to the car. Granted its not totally steal proof but it will make that much more of a bitch to remove.