Tell boy that digging a hole is good exercise. Make him dig it rather large and at least 3 feet. Then tell him that cementing the sides and bottomis good exercise, remind him he should use rebar. Then tell him that cementing around the hole is good exercise as well as a cover over the hole. When he is done tell him that it seems he's built a pool with a cover to protect you from the sun and see if he would like to start exercising now ;)