I have a sign over my door saying "May this house be safe from tigers". Thus
far, it has worked like a charm.
Maybe something similar will work for your boat. ;-)

Or, to put it another way, the threat to your boat from terrorists (who are
always pictured in the US as desert-dwelling landlubbers anyway) is probably so
small that it is insignificant. Like trying to protect your city-only car from
passing elephants.

Steve