You should consider a GPS vehicle tracking device like this one.
http://www.airiq.com/airiqnewweb2/portal.cfm?chapterID=23
GPS units are good but don't let anyone know about it. Put the car in a container or steel truck and it's all over red rover. GPS can't penetrate the steel. So if you do get one, keep it secret, don't even tell your friends. Not that you can't trust friends but a slip of the tongue or a drunk burst of voice, word gets around and any would be car thieves can plan it out.
I run a tilt sensor for the protection of towing. My sensor sits under the console so is nice and central, if you lift the car or try to take a wheel at some degrees (forget what it is off the top of my head) the alarm will sound. As they say, at the end of the day, anyone who wants your car or wants to know where the car is,
WILL find out. We just have to do our best to protect our cars. Alarms aren't to stop them, just to give them less time at doing the theft.