That's what they make garages for. And dogs. And shotguns.
Same with me on temper.
dont know if someone already mentioned this, I only read the first page, but when I was an apprentice auto elec, we played a trick on one of the guys at the workshop.. You just wire a coil to the seat rails via a change over relay connected to perm power, which switches off when you turn the igntion on. The coil firing is triggered by a push button switch mounted in the seat. Just make sure you turn the ignition off before you sit down..
Or a Rottweiler.. active alarm with intruder immobilisation :)
or some of these might give you some inspiration:
i have been thinking about the same thing for a while, I have a 1969 dodge dart gt convertible restored to original condition, which gets a lot of attention. the only thing i would do differently is have an audible warning whenever someone got within a few feet of the car, in three different languages at that to be sure to avoid a law suit!!!