I just saw a video on instagram of someone basically sabotaging megatrawlers by dropping gigantic pieces of marble into the ocean to mess up their nets. People who know about fishing: does this seem like it could be effective or scalable? If so it seems like it could be massively cost-effective. 

Link to video: https://www.instagram.com/reel/C3QSQTdvDQh/?utm_source=ig_web_copy_link