I'd like to see someone make something like the retractable key rings you wear on your belt. Your Boga could then fit into a holster worn next to it.
Those work off of a coiled spring design. Salt would destroy them far too quickly. I think you'd be better off with a coiled lanyard and a fly-fishing style magnet attachment. Magnet keeps it on your belt, and lanyard allows you to work with it. Neither would suffer from the salt exposure like a retractable cable.