Okay well there enlies the problem then cause my drain layer will be completly submerged. Thus creating the pond... if I just kept the layer of mud in the substrate layer that would be fine. Idk I know this take is going to def take me a couple months that's for sure. Maybe some experimenting is in order.
If you allow the mud to harden will it stay hard? I know once clay hardens tit takes a lot to get it to soak again