Some trailer owners are convinced that someone will pull the ball mount out of their hitch receiver, and thus they need the ball mount pin (such as any of these at eTrailer
) to lock as well - we have one of these, and I have used it on trips.
There are kits containing both a latch locking pin (as Chuck mentioned, such as this Master Lock
) and a ball mount locking pin that use the same key, to keep the proliferation of keys down; here's one set
(big one for the ball mount, small one for the coupler latch).
The coupler locks are likely easy to break, so deter the more determined thief, some people resort to a coupler lock which occupies the ball space when unhitched, such as these at eTrailer
. The number of keys is really getting out of hand now, so you can get all three locks using the same key, such as in this MasterLock set
Even more extreme are wheel locks (like a Denver boot that you put on voluntarily)... there are many kinds, such as these The Club units at eTrailer
. I think those are typically only used for trailers left unattended in storage.
I think you need to assess your own level of paranoia and equip yourself appropriately. No security locks of any kind are actually required, but most people seem to use at least the coupler latch lock, as Chuck described.