Re locking bikes to rack:
When going to an event I always try to park beside the guys with better bikes.

Otherwise, when out in places where I'm concerned, they get stuffed into the back of the car. With my rack I could run a cable lock through it and the bikes if needed.
Re locking the rack to the car:
I've seen locks you can put through where the bolt goes but since mine is suck a

to get at I've never worried about it. IE: I have to unscrew the bottom of my bumper, pull it away from the hitch then install/uninstall my hitch then put the bottom of the bumper back on again. The plus side of this is my hitch install looks stealth when the rack isn't on the car.