You should add whales to the game! Have them come around once in a while, and they risk breaching out of the water and smashing into the raft. If they smash the raft it'll take out like 3-5 foundation. You could add an item to deter whales, and you could also kill and harvest them which would take a long time. If you kill the whales you can get a ton of meat, and blubber which can be used as a new crafting item (maybe as bait for the fishing rod or something). Also if the whale carcass is left out for a while it'll attract a lot of sharks that will eventually go away.