Since the biggest mess of cleaning a fish is gutting it, I opt to gut some bigger fish while still in the water. No law against that anywhere. Made the mistake of gutting a 60 pound black drum one trip - right on the floor of the boat. I'll never do that again! I add this picture to show you something. While in Sitka, Alaska, I fished for salmon. This picture shows a trough that is affixed to the railing on the boat. On the way back in, after deep trolling (400 feet of water) for king salmon, the mate would put a salmon in this trough upside down. He then gutted the fish and all the mess and blood stuff went overboard rather than into the boat. Note the back piece that is cut out for the fish's tail. I know this is for salmon, but something like it could be done for other fish. A rock would fit in there nicely! Obviously the fish had been dispatched with a club before being laid in the trough. I should have taken a picture of the fish in the trough but I guess I didn't. I'm still looking - if I find one I'll post it.