Yep - there are roof racks and hitch racks that lock. My Yak roof rack locks to the roof of the car, and then each fork mount locks. I've only ever left bikes on it overnight at my dad's house (in the middle of nowhere), but I don't worry about stopping to eat. My hitch rack has a cable lock. I worry a little more about that one - but still it's OK for stopping to eat.

That *is* the nice thing about the Element - at the MS ride and other similar events - just wheel the bikes inside and lock the car. Pretty cool.