Theft-proofing a convertible with no steering lock

Similar thread on an Early Bronco forum.

Lojack requires effort, awareness and equipment on the part of the LEO's to be effective.

Something mentioned there that I've not seen here is a variety of GPS/cell phone technologies that A) can tell you where the vehicle is RIGHT NOW, B) set up a perimeter 'fence' that sends you an alarm if the vehicle moves outside of it, C) in some cases can remotely kill the ignition/ECU/fuel pump etc. I looked into it a little, don't know a whole lot about it, yet. Apparently some car rental Co's are using these systems.