Originally Posted by txmatt
.... I don't lock my boat, but I also don't keep anything in there I couldn't stand to lose.
There's some good advice right there.
FWIW, we have a full-length stem-to-stern boat cover that hangs off the boom and is held down by s-hooks and lead rope. Since (pointed out already) thieves tend to be opportunistic (and often a bit thick) if they can't work out how to physically get on board, hopefully they'll give up and go home.
Sure, the cover might be a pain to get on and off, but it does keep the brightwork bright and the bird-poo off the deck..