Cheap family fun
Ok. Don't laugh. Last weekend me and the wife and kids painted rocks. Yep, that's right. Plain old rocks that we found in our landscaping and a few more we grabbed at the river. I was skeptical at first. My wife had to convince me to join them. And you know what? It was actually really fun! It was like an at-home version of sip and paint (I was absolutely enjoying a few coldies - makes art better).
I live in Laurel and did you know there is actually a Facebook group of people in town who paint and hide and find these rocks? I don't know if there is one in Billings, but feel free to check out the Laurel MT Rocks page and steal the idea.