Andy, he's bored. At that age, they have a huge need to express their urge for discovery and expression. I'd get him a huge stack of paper and some multicolored non-permanent markers and let him go. Throw in some praise here and there, and watch what happens.
Years ago, I was a field service rep for Xerox, and had access to lots of used paper, which I'd take home to my children occasionally. Man, they loved it! And guess what? They all amazed me with their creative talent.
Paul, what a neat little dog. And the look on his face

No wonder why dogs are man's best friends.