I'm making a small box for my 4 yr old son to give to a friend who is moving away. I want to figure of a way to write their names on the wood in a manner that he can help. E.g. "Carving" by using a hammer and nail to trace the letters. I would like something more permanent than simply painting. He can write both of their names - issue is method of making it permanent. Any ideas? Hope the question makes sense.