Sorry. Imagine shooting at waterfowl, concealed in a squarish wooden "tub" below water-level among decoys, with only a few inches of freeboard. It was common on our offshore but only used in a few places now. Current tubs are made from plywood covered with fibreglass, weighted at the bottom. Scare you to look at them but never heard of a fatality. Deadly, migod, deadly. We could almost reach up and catch them by the legs.
In American English, that's called a "sinkbox". It's been illegal in the US as long as I can remember, precisely because it's so effective.
