The fake LEDs are actually a pretty good deterrent but I've also seen stickers that simulate rust and scratches.
Something else to think about is the catalytic converter a friend of mine had it stolen off his car because it has good scrap value. One way to fix that is adding a set of wires from the battery to the CAT then when you come out in the morning and see shoes sticking out from the car just call the cops
JK.
Seriously though if you want to add a kill switch to the ignition instead of using a normal mechanical switch get a magnetic reed switch glue it under the dash some where then you can only start the car by putting the magnet on the place you put the switch.