Here is our latest rock project. Tick tac toe!! The rocks are small beach rocks and the slate has a longer story. A church near my parents house got rid of their slate roof about 20 years ago. My mom noticed walking the dog in the woods behind it that they still had a huge pile of slate shingles. With the permission of the church she has been taking them and mostly using the large pieces to serve cheese and crackers on. The small pieces have been tossed until they became the perfect game board.
We have found that nail polish works great! It comes with a build in brush for easy clean up. It is very durable and glossy. Alex toys have particularly good nail pens.