I've done several coastal cleanups. In general, things like metal or plastic signs, golf balls, metal debris, fishing gear and tackle, etc. is trash that won't benefit marine life, particularly things like lead fishing weights. Plastic bottle tops and especially plastic don't do much good for the marine environment, with plastic bags more likely to kill critters than provide a safe home. Lots of other things provide some kind of home to sea life and you should give some thought before ridding the ocean of such. At one coastal cleanup, I pulled a partly buried folding chair from the sand, and an octopus came out with it and quickly darted away. One man's trash is another sea creature's treasure