I know it's your dad's car and all, but the first thing I did when I bought a car is get a Car Alarm w/ tilt & shock sensors and battery backup. Afterwards, then get the wheel locks just to give them extra 2 minutes of the alarm tripping.
I'm currently working with my friend who's a electrical engineer to find good and reliable places around the car to put mini Piezo sirens around the wheel wells. That way, even if they tried to go through the wheel guards, they will be getting the biggest headache of their life.
This is what I'm working with at the moment.
http://www.youtube.com/watch?v=Duwak...eature=related
I tested it on the Z's wheel well...holy crap, high frequency & echoes. Only 10 seconds and I already needing Tylenol for 2 days.