Line locks that will stay engaged with no power to them are very, very expensive. They're used in heavy equipment as parking brakes, and they used to be around $80--but then the Feds stepped in and said they have to have pressure-loss alarms. Last I looked into 'em, they were over $400. Still cheaper than losing the car, I suppose.
I had a keyed switch in the console of the Black Bitch to turn off the electric fuel pump. They would've gotten a few blocks on the fuel in the float bowls, but then they'd be dead in the water. Then again, that car never got to the point where anyone would want to steal it, so even that was overkill.
Hidden switches will work as well, but the simple fact is that if it's being stolen by pros, they're gonna get the car. A car they can't start is no match for a roll-back truck or the ease with which older cars can be hotwired.
My single-best suggestion? Park it with the steering at full lock and put a Club on the steering wheel. Install the Club with the long end pointing at the corner of the trans tunnel and floorpan... yes, even in the garage. Nothing's foolproof, but the Club is not only an ounce of prevention, it's a pound of deterrent. Any thief will know the car's gonna be a chore to steal and will likely move on to an easier target. Being tricky is always fun, but sometimes being obvious is more effective.
