The club, instead of leaving it easily accessable from the front, turn it around so that you have to lock it with your key between the steering wheel and the instrument cluster.
The brake lock things tear up your carpet. I speak from experience.
I think that remote cut offs are the best bet. Something underthe hood inaccessable, and hidden.
No Benzes in the stable at the moment, but itching for one again.
Former Mercedes in the Stable:
1983 300CD Turbo diesel 515k mi sold
1984 300CD Turbo Diesel 150 k mi sold
1982 300D Turbo Diesel 225 sold
1987 300D Turbo Diesel 255k mi sold
1988 300 CE AMG Hammer 15k mi sold
1986 300E Amg Hammer 88k mi sold
1992 500E 156k mi sold