A friend of mine had his aftermarket stereo stolen at the Metra train parking lot. He replaced it then had that one stolen as well. Well the only way to get it out was to reach behind it, as it was mounted low, and pull it out. We devised a row of razor blades attached to a small thin wood block and glued that to the back of his 3rd stereo. He came off the train one day, noticed his door ajar, the front seat covered in blood, and several fragments of fingers laying on the floor. That is how you teach a thief a life lesson. Good fun.