We use the same as Robin.
IMHO, locks only serve to make YOUR (whatever) harder to take than someone else's. If a bad gui REALLY wants YOURS, he will get it.
And, locks also serve to "keep honest people honest" - takes away the crime of opportunity. For example, taking the keys out and locking the door to your car is in this category - prevents someone from just walking by and going... WOW - let's jack that 'vette... the keys are IN it... oh YAH!
Putting an alarm, ignition cut out switch, and other elaborate "locks" fall
into the first category above - to slow down and / or deter a bad guy INTENT on having a nice, new 13' Scamp.
B-T-W, I like Brian P's idea.