How do I prevent an egg cracking while hard boiling it? Sometimes when I cook hard boiled eggs they will crack in the saucepan, and some of the egg will seep out into the water.

Am I boiling the water too vigorously, or can I add something to the water to prevent it?
I used the method here before with good success: http://simplyrecipes.com/recipes/how_to_make_perfect_hard_boiled_eggs/

Basically you start with the eggs in the pan with cold water and bring the water to temperature, right when it reaches boiling you pull the heat back and let the eggs cook for 10 minutes.

You don't need a full on boil to hard boil the eggs.