We want to put a koi pond in our backyard. I saw a nice design that someone used - it was rectangle, 6x4x4. They built their pond three feet deep, sunk it a foot into the ground and added a foot at the top in clear acrylic for viewing. Is there any reason we couldn't do the same thing, just sinking a clear acrylic tank (6x4x4) a foot into the ground, then build a two foot wall around it? It seems a lot easier and more secure than piecing all of these elements together and trying to seal everything properly.