Cars that are post-1980 in make and cost more than a few green chips have a feature called the "Valet Key". A special key that only operates the ignition. The trunk release, glove box, and center console (new cars have compartment in the center armrest that locks now!)
locks do not work with this valet key.

Don't know if the 20/20 show (Didn't see it sorry), was about Valet's being able to override this security feature.

Or you could try the special "SOTSOG Security Feature". Carefully explain to the punk parking your car that if they decide to take anything, they better make sure to get ALL the guns hidden in the car, at least that way they will have time to get out of town before you come back with more from home.