Fender socks often work themselves off in rough weather, so you may not have been a victim of theft...
And I'm sorry to say, in relation to the first post, that I get very annoyed by people who leave dock gear in awkward places on berths - when I move to a new permanent berth I always clear any detritus away... Did you check with the new berth-holder that he hadn't removed it?
-------------------- But no pleasure is comparable to the standing upon the vantage ground of Truth.
(Francis Bacon)