thanks so much...now going to read about leaving the rocks.
oops, when i clicked on your link, it says PAGE NOT FOUND
A quick search: http://www.4onatrip.com/2012/07/25/roxaboxen/It comes from the children's book "Roxaboxen" where the author's mom and neighbors built a town with rocks and boxes when they were kids. Visitors are encouraged to decorate with rocks and leave a rock from their state, very cool.
These stones are so lovely. A sense of intimacy.
Fun. I remember doing this with my kids.