Damage to the Headstone is covered by most Home Owners Insurance. It does not have to be listed separtely on your policy. (Check with your agent)
To Clean a Headstone:
1) Wet the stone thoroughly and do not let dry until you are completely finished.
2) Use a mixture of 25% Bleach and 75% Water.
3) Using a brush start at the bottom of the stone. Remember to keep the stone wet.
4) Rinse the stone with clean water