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Maybe not THAT extreme, but I did bury my hydrophone in my compost pile. It's out on loan, but I figure I'd need to let it sit for a few days before recording with it, and then would need to do so for a few hours to see what I could get...the initial session was too short to get much cool stuff.
I tried putting the hydrophone inside a balloon filled with water to get interesting impacts, jiggles, etc., but unfortunately I couldn't figure out a way to avoid cable vibration/noise emanating from where it touched the tied neck of the balloon. Made some interesting sound though.