Don't worry-it's only a rock.
We have a medium-sized permanent puddle at the beginning of our driveway that we occasionally allow the children to play in. This has caused, on occasion, strangers to pull over in their car, park, bring the child to the door and inform me they were playing IN MUD. IN THE STREET. (In reality, a car would have to veer completely off the road and into our driveway to hit anybody.) When this happened, I replied to the stranger, "Oh, he's okay-Owen! Don't forget your lighter!" (Not really the second part. That was said in my own mind.)
I happen to be a firm believer in Mud Party memories.
Tiff and Jeff-Mud Party 1985
Even if it takes you an hour to clean up, causing you to push back your trip to the grocery store, causing you to run into a boy from high school who has witnessed you fail your driving test in a number of humiliating ways, only to then witness you drop a glass jar of marinara sauce over your sandaled feet. Even then it's worth it. Practically.