I use the same lock as rockhillmanor, but I put one on the hitch and just one on the toad. It prevents someone from stealing the toad and fully disconnecting. With the backup camera it would be hard to miss that the toad is half connected. I like the pins better so this was my compromise.
I think most cases of missing pins (especially if just 1 pin) are human error. My pin has a spring to keep it closed. Also, it has weathered (mild rust internally or dirt) so that it tends to stick closed (which is safe) but I guess it could easily one day not pop-out and the pin could be stuck open.
I think that is what generally happens to people.. they lock things up but dont give them a nice inspection/test.
