Welcome to 2004 when thieves began using roll backs and fake repo documents.
For years I always unplugged my distributor but left it looking like it was plugged in...even if a thief was dumb enough to take the time to look under the hood. Pulling a fuse helps too but everyone has caught on to that too. If the car cranks and doesn't start it's either a fuse, a relay, a kill switch, or something is disconnected. It takes time to diagnose what it could be if a car doesn't start.
There's only two things you need though. A good alarm that alerts the owner and a GPS locator installed in the car. $10-20 p/ month for the service and you'll always be able to track the car. I'd rather have the car taken and them caught then just a broken window or jacked up locks every time.