We've found two, searched for three -but I suspect it was missing due to recent hedge trimming.
We enjoyed them, and would certainly try for others.
We don't have our own stamp. If there were more LB's around us we would be tempted to get one sorted!
Is it possible to chain the stamp to the box? I've seen it with a TB, you can look at it, get the number, but other than walking off with the cache box (it was an ammo!) it is sort of obvious the TB has to stay.
G