I would like to do something like this. I have a steep grade next to my house. It is county land, so I'm trying to minimize cost. The water runs off really bad. The slope provides access to the side of my house. The current stepstones are basically sliding down the hill. I want to have a dry river bed with step stones in it or along it, so that someone can step their way down the hill while the water rushes down it. Do I need to mortar EVERYTHING into place?