... Or you could use a float on the surface with a sinking type line. That's what I've done but only twice. It complicates anchor recovery if you don't snag, and I don't like the added risk of a passing boat snagging and tripping the anchor. If I had to anchor someplace like the East River in NYC I'd do it again, because I wouldn't ever want to swim in that water and who knows what (or who) is on the bottom?