Head Shoulders, Knees and Toes
Players each have a ball. Coach tells them 'how' to stop the ball when he yells stop.
Players will dribble until coach yells stop. Then players will stop the ball with certain body parts (ie elbow, knee, foot, bumper (butt), etc)
Move around the field so they need to look in different directions to find you.
This time point on your own body what they should use to stop the ball... don't verbally tell them.
You choose the body part to stop the ball. Have a player decide when they want to yell stop. They will need to yell loud enough for all players to hear.