the headlight kill switch is pretty good actually. or brake light kill switch. cars will get pulled alot faster for tail/brake lights out it seems. plus i'd rather have some random person slam into my car with the thieves inside, fuck up their necks (thieves probably never wear seat belts because they are scum).
basically the best things to do are:
-fuel pump switch, hidden. if possible somewhere hard to find. in the trunk, hell, use 2, and have one that's semi easy to find for daily use, and one thats hidden. if they find the "easy" one, and the car still doesn't start, they'll think the car is broken or something.
-ecu switch. much better than a battery switch, no one likes resetting radio presets and clocks all the time. if anything put it in the glove box and lock the box, or behind the glove box, but where you can get a finger up under the dash to flip it.
-steering wheel quick release. just about the #1 method against punk kids and joyriders. vice grips on the hub can work as a steering wheel but its not easy and punk kids arent expecting to see no wheel. they'll pass on that.
-removing a vital fuse or igniter chip or unclipping something from the harness. maybe even a MAF sensor so it goes in limp mode. this is more of a method for when you're away longer.
the best way to avoid it is to keep valuables out of it and not let every joe shmoe look at your engine bay at meets and stuff. thats where people scope out.
the ideal tactic is to make the thieves spend as much time as possible trying to get in the car and get it running. the longer they take the more chance someone will see them or they will give up.
and carry proper insurance. if you have quality parts on your car, have it appraised and pay a little extra for the aftermarket product insurance, at least for some of the larger stuff.
and my favorite method:
dont daily drive a super street car. if you have a car that is all painted and blinged out and has a gajillion HP under the hood, garage it. or at least lock that bish up during the week.
most 240 owners should be thankful, thieves like super duper JDM cars and stuff, they usually wont try to steal the beat up multicolored s13 that is common around here....unless someone sees $6K worth of engine work under the hood.