We are constructing a stacked stone mortared wall, the wall is approx 6ft tall x 20 ft long and we will be building in a spill way to create a water feature which will be at the top of the wall, falling down over the stone to a raised pond. We have looked into using different water tight mortars and also adding a pond liner within the wall. The spill way is approx 36" and will fall down over 5 ft section of the wall. We worry about the water finding its way back through the wall and mortar, has anyone done something like this? Can you give some advice. Thanks in advance.