I began putting the river pebbles on the dollhouses foundation. Make sure you paint your foundation first in the base color you would like to show through between your pebbles. I used the same dark brown as in the rest of the dollhouse so that it blends invisibly between the pebbles.
Use tacky glue and turn the dollhouse on it's sides as you work your way around the foundation. It's actually faster than having to put these pebbles one by one with hot glue. Also, the dollhouse is much lighter than it looks so there should be no damage in positioning it on it's sides right now. I was able to lift and turn the dollhouse all by myself and I have a bad back. It's extremely light weight despite its size.