Huge piles of bois d'arc are the best I have found. cup hooks cemented into about 2 gals of concrete. chain from the cup hook to the object to sink.
They do like the bois d'arc trees, they last forever. The hard part is cutting one down, I tried to cut one on the lake with my chainsaw, I went at it until the saw got hot and quit, the tree is still there with a burned cut in it.