what you do is bolt the bloody thing with 5mm thick alloy clamp to chassis using bolts with these heads:
if I had really expensive stereo I would make a thick alloy plate with barrel locks to go over the top of stereo (which would bolt on to chassis as well with the bolts from above)... De-lock the car, security tints, high voltage sign warning that if someone breaks in get shocked, warning sign that breaking in the car is a serious risk to health.
Unfortenately we can't treat russian way the bloody thieves.. and assult is more seriuos crime then theft...
BTW in russia there are almost none of joyriders, only proffesional car theft, and when they break in and steal cars/stuff, they don't damage merchandise.
There was an article somewhere, how the wrong car got stolen (actually from wrong owner), when thiefs realised that they are in deep shit, they washed the car, returned to location where they stole it, and I think they left some money in it for compensation...