I started placing the river pebbles on the dollhouse foundation. First, make sure to paint the foundation in a base color that you want to show through between the pebbles. I chose the same dark brown used throughout the dollhouse so that it blends seamlessly.
Use tacky glue and turn the dollhouse on its sides as you work around the foundation. This method is faster than applying each pebble individually with hot glue. The dollhouse is surprisingly lightweight, so moving it onto its sides won't cause any damage. I was able to lift and turn it by myself, even with a bad back, because it is much lighter than it appears.