they are actually glass racks. they fit together much like milk crates do. we then zip tied every one to the ones around it. the pond was only a foot deep. there was no flexing at all. any other questions please ask will do mu best to explain.
Due to using my fish supplies and what was readily available to us at work we only had to buy the zip ties for $15. the liner cost me $100 im not even sure what the crates would cost you to buy how ever you could do this same thing with milk crates however due to smaller sizing you may want to add some bricks for weight.