An old colleague of mine had the tape player pinched from his car (early 90's)
so he replaced it
And it got nicked
So he replaced it, this time taking care to araldite stanley knife blades inside the top of the cassete slot, with the sharp end pointing towards the front of the car.
3 days later he found the passenger window smashed, but the stereo was still in there, along with 3 fingertips which had been used by their previous owner to try and pull the stereo from the dash.
Never had a spot of trouble after that, strangely enough.