stealing our cars is very easy you don't even need the key the start the engine.
a kill switch is a good idea.
i've been to car shows where people have had their air cleaners stolen in full view of everyone and nobody said anything.
That's the problem - you could easy do something electrical so the car does not start immediately and that will cost worthy minutes. But on car shows it seems to be normal that people with older cars are working on them. So nobody will take more attention - and even if, when the theft is eloquent, nobody will pay further attention though. Except people there know your car and know YOU but that is a challenge on big car events.
And even if you have a hood latch which could be only opened from inside - the frameless attached window-glasses could easily been pushed down by hand to reach the door pins...
It's a mess - if you are proud of your car and folksy it is some kind of risky to show your best piece (the car!)...
Otherwise: my car have a locked ignition lock originally. You have to turn the lock with the original key to unlock the steering wheel and so it is the same with the transmission: it is locked in the reverse gear, too. So you could only drive backwards and straight without the right key
I think this is a special feature of the T5's built for the german market. Our registration office requires that also for new cars back in the days...
Don't know how to conquer that in a quick way but that seems to be too much detail for a open forum like this perhaps read by the false people... So beware of too much information on security gimmicks here!
I think it is better to don't let you car to much out of your eyes. Better put your bad-tempered wife or girlfriend in front of your car - she will kill everybody who starts to put his fingers on anything or start to talk to her