We don't have many sharks here in Ontario, so we've never had to worry about using anything more than a stringer for the fish we're keeping. I have heard of pike or even snapping turtles taking a fish off a stringer, but it's not common enough to worry about.
I guess if we get the chance for some saltwater fishing then we'll need to think about what to do with the keepers.
Kayak Deck Gear Bags
Kayak Motor Kit
YakCatcher Rod Holder