This is What I did in my pond that worked well. I bought eight food grade barrels that tapered at the end and filled them with large river rock(100lbs) and some very large stones. I drilled multiple holes at the top so that the air would escape. I was able to float the heavy barrels out into 4 ft of water and submerge them that way( open end facing the pond). I tried filling them with a 100 lb of pea gravel in an earlier experiment but something kept on knocking the gravel out which made them float. I measured 4 ft on my body to know how far to walk out to submerg the barrels.I also used a 2 wheel moving dolly and a piece of plywood to get the heavy barrel into the water. Oh wooden boxes would probably be easier but it was more costly. I bought the used food grade barrels off if craigs list $5 each. I hope this helps someone, enjoy!