An out of left-field idea. It doesn't happen a lot, but one of the things people fear deeply is being bitten by a shark. Sharks sometimes bite surfers, because, it is suspected that 4 paddling arms lying on a surfboard triggers the "tasty seal" match in the shark's brain.
(Reportedly sharks don't actually like how we taste that much, and have spit out human limbs they bit off. I dunno, but somehow that's adding insult to major injury.)
Anyway, to stop this there are some products on the market. One is a set of decals in the black and white stripe patterns of poisonous fish sharks don't like to eat. Another is a set of electrodes that send out a strong electric field which sharks hate (they have electric sensing organs that most fish don't.)
Here's another idea, for all the surfboard shark repellant readers of my blog out there. Since the shark looks up at the board against the glittering surface, patterns on the bottom may not be enough. But what about new bright but low power LEDs? Possibly an animated pattern moving over the LEDs to say "not food" to the shark. First of all such light is highly non-natural (at least not from prey) and can be made to move in very artificial ways, or natural ways that signal non-prey. And today, the power for it is not very much. Here's where we need the advice of all the trained icthyologists reading the blog.