lynn- what works for me is simply to lock in a spare ball in the
socket, so it is "occupied".
I discovered that my hitch lever, even if locked, will allow it to be
dropped onto the ball.
(My trailer came with one of the hitch locks, that also did not fit).
So now, I insert a spare hitch ball, then lock the lever with a
padlock. Unlikely that somebody will spend the time trying to line all
that up to fit in a receiver to take it away. But as they say, if
somebody wants to steal it,they will find a way.
Jere Potter,
Fort Collins, CO