Basically, your options are switching the:
1) Starter
2) Ignition
3) Fuel pump

If you are really paranoid, you can do all 3...

As an aside: I once saw a device that was basically a one-way check valve on the braking system that you could enable. Once hydraulic pressure built up, it would not release, so the braking system would essentially anchor the car in place.
I would have to wonder where your car would be abandoned with these types of 'latent' devices, however...

Best of luck.

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1986 300E 5-Speed 240k mi.