Start by creating a No Man's Land with cones about 10-15 yards wide by 30 to 50 yards wide, depending upon the age of your players.

Place your defenders and back midfielders in the square, with your attackers outside. The attackers job is to get through the square without loosing possession of the ball. If the defender gets the ball, he gets to keep it until the end of the game. The defender with the most balls wins. Each game should only be about 3 or 4 minutes with a 2 minute break.

Use the break time to show them how they lost possession, or how the attacker managed to get past them. Usually its poor body or foot positioning. After the rest, play again. You can switch attackers and defenders so all the players get equal touches.