I'm thinking 10'-15' of line, a large stainless ring on the maind sheet, located between the beam and traveler (or maybe located in front of the traveler cleat), then attached to my harness with a carabiner.

Pine Island sound has a dense shark population, it is a nursery for five different species, iirc. Also, large hammerheads are legendary in Boca Grande Pass. But my real worry is hypothermia.