That’s kinda my plan here. I was just thinker tuck under because of how funky the edge of the liner is where it was attached to the biofalls. Here’s a pic of the front/pond edge of the bog box. I was gonna use one row of timber and dig down from there because if the odd shape I need I thought it’d be hard to build a structurally strong box on siteWhat I would do is build it up a bit 10 inches or more above the pond edge. Tuck the new liner OVER the pond liner. The water will waterfall into the main pond and most likely will not leak.