Right I get that, I guess the "stacked vivariums" if you built a tall enclosure with a 6x3 footprint would the entire bottom need to be water? With something that size the weight and filtration would get difficult. Any of the acrylics or poly will get scratched and fast, so that leaves you looking for glass...Say you built a 6x4 foot print and put in a pond liner for one side you would be able to see from the top down. I don't really see another way around it...