I also have thought of doing something similar to that.

I have a bunch of old water "plassons" (chicken or turkey waterers) that are made of plastic and are slightly positively buoyant. I thought about tying a bunch of these into something like a bouquet of helium balloons would be, then anchor them like you said with a concrete block.

I do not see why it would not work well. If a person hooked it it would have some give.

John

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