There was a good product on the market a few years ago called "Shark Camo".
It's essentially a large striped sticker you put on the bottom of your surfboard giving it a "stripey don't mess with me I'm full of poison" look.
The theory is that sharks know that most stripey fish in the ocean are poisonous to eat. So if they see a big stripey fish/seal floating in the water (surfboard) they will be deterred. They actually had some footage on youtube of how effective this was when placed on a bait that looked like a seal. The sharks investigated it and then turned away whereas prior to having the shark camo on they devoured the seal shaped bait.
Apparently the US army bought the patent to shark camo for their marine divers and Shark Camo was taken off the market.
Also many surfers found that although they were never attacked by a shark, as they exited the water, they were mauled by lions as the large stripey look made them look a lot like a nice fat Zebra.
