Fit a nitrogen bottle in the boot hose it up to the interior with an electronic valve wired to open when your alarm goes off, they will have to drive the car as high as a kite or lift it, I don't think you will stop them lifting it unless you have airbag suspension that drops the car to the floor so it's arches are near enough sitting in the tyres and turn full lock to one side to make it a bitch for them if they are winching it into a flatbed but as said above if they really want it they will come prepared