The last two cars I had before I bought the truck I have now, I spliced a switch into the fuel pump wiring and expoxied the switch to the back side of the brake pedal. It was a push on/push off switch, slide foot under brake pedal and pull foot back to operate switch. No fuel pump/ car no go. I also use to have switch to kill the taillights on my Mustang, but that's a different thread. As far a preventing a smash and grab, that's a little tougher. I have wanted to get some of that window film that prevents glass from shattering with impact to thwart that route. As soon as a I can figure out how to put some magnetic locks on the doors without spending a buch of dough I'm going to try it.
In the past I've also put in master battery switches to completly kill all the power to the car but having to fix presets all the time is a bummer, and I'm not sure how the computers in cars today would react the losing all power on a regular basis.