secondary alarm seems like it would help for this particular instance. Since they pushed the vehicle out I'm thinking it was towed away from the scene, so a "secret" hydraulic brake lock would be good too (ignition switch wouldn't have helped).
Security (aside from ratmobile) can be had through a certain degree of obscurity. The thieves knew where to find the horns, so don't be so predictable. Though I would leave the stock horns as a "honeypot", if the alarm goes off and they thought they disabled it, the surprise alone will probably scare them off.
There is motion detection software too, since they have a camera it would be simple enough to have an android app that pops up any activity on your phone and streams the video to it, call the cops, get 'em off the street. Just don't call the cops on the postman
