As mentioned above..if they want it , they'll get it.

But to ward off the punks, I use a Clfford alarm with 2 sirens and a battery back-up.
When I have to park in the city, I remove the positive electic socket under the hood that disables it from starting.You need one of these plugs to start the car or else....
And aside from sleeping in it, this is the best you can do.

Good luck