Hi, Your child asks a very good question. As we worked down we make sure to keep a strong foothold with a ledge like a paddy field compacted with lots of water. The sand gets compacted as we walk up and down the ledge. For the parts of the sculpture already finished we spray them with a very dilute Kids glue on the surface and this holds the surface grains together and protects it from drying our and also from the rain. It doesn't add any strength but just preserves the detail. Thanks for your comment.