How to prevent someone taking my vehicle if they have a key
Prevent someone taking my jeep when they have a key
Got power but car wont start
Three possible ways I can think of: (Disclaimer; I'm no mechanic) 1) Disconnect the battery. 2) Remove the fuse for the ignition / ECM (computer). Determine potential side-effects BEFORE you try this, check your manual, find the correct fuse for the ECM and pull-it or run a 'secret switch' from that curcuit to effectively disable the vehicle when required. This will also shut-down a vehicle that won't turn off due to something like a defective ignition switch. WARNING! Be careful, do your brand research and consider the fact that you'll likely lose your clock settings (at least), possibly disrupt your security system and can even potentially lock yourself out of your own security system, similar to removing your battery in some vehicles. 3) Install a security system. Even a cheap mickey- mouse system that requires a fob or code to start. (better to have it installed by a professional) DO NOT under any circumstances, try this with any BMW product - ever!
This is usually a question from people who owe back payments on a car; to keep it from being repossessed. There are really no options for this. The repo man will just call a tow truck. You might chain the wheels together or to a tree, but a repo guy usually has bolt cutters. He has a key, so anything you do to disconnect power, he can override..... If your particular interest is just dealing with an ex-wife who has a key, you could re-key the car, or install a kill switch in a hidden location.
They probably also track your car so you can't hide it.
I get the Repo thing, for practical purposes they're virtually un-stoppable. I was thinking the question related more to an armed services member or worker leaving town, possibly an 'ex' or a pesky friend/ family member that just won't give-up... which, come to think of it, the latter are probably just as determined as the Repo guy.