Remember to use the slapshot to clear the ball when you are under pressure in your own zone and you know your teammates could use a breather. Watch this defender clear the puck successfully in this QuickTime Movie (1.5M).

If you must block a ball, hold your stick at a very low angle close to parallel with the ice. This way you have the surface area of the length of the stick to block the ball instead of just the head of the broom.