We called them clappers. They were dumped down the free-fall chute in the sono package. Drove Russians nuts! They had to surface to pull them off the hull.
The Soviets didn’t have titanium hulls on at least some submarines?
I can see those things being dumped by the thousands with little pingers on them. They would have to die sometime though since if they didn’t the ocean would have to be littered with little pingers. Clappers and simple and cheap though.