Parents of human children learn to deal with cuts, scrapes, bruises and bites. They learn to recognize when professional medical treatment is called for.
We used a pair of baby scissors with blunt ends to cut away the hair and remove the stone. Then I soaked the foot for a few more minutes. When we brought Sky upstairs, he climbed onto the couch, flipped over on his back and slept for the rest of the evening. I haven't seen him pay any attention to the foot today, but I will soak it again tonight to relieve the irritated skin.
I don't hesitate to call the vet if something is seriously wrong or even if I just feel something is wrong, but for summertime scratches and scrapes, common sense works just fine.