I like the bags. Good idee. I wonder how that would work with bigger structure, like a 6' tall cedar tree? I guess you could tie two bags on. The bags would offer several benefits over blocks. They wouldn't scratch up the boat and you could fill them with dry sack-crete and it would cure once it sank. With some strategically placed steel cable through the bag and sack-crete, it wouldn't matter if the bag did decay.