You don't need a heavy river anchor, instead, this Danielson Galv river anchor might work for you, it's small but obviously 3 pounds so it's heavy duty. When it was out in the lake, it started with the 4 of us, probably around 600-700 pounds in total, the anchor kept us locked in the firm. I suspect we slipped a bit closer to shore but it was hardly noticeable. It is sturdy and apparently stronger than suspected!