i bought pond pebbles from home depot and i used clear sillicon aquarium sealant to piece it together, sorting out flatter pebbles then i added each one and used a blow dryer to set it, rinse.. repeat. there are a few small holes that allow water and a little bit of sand to come through a maze in the pebbles (i hope the water flow is sufficient for the filter to clean the water on the sand side too but i'm not sure yet, but most holes are sealed. i dont really want sand flowing to the side with the filter. i have small pebble gravel on the side with the filter. here is a picture of the dam and the ramp after i finished setting all the stones in place.