Decks and wood patios have to endure quite a bit of wear and tear, e.g. if you have trees around your house. In the city of Toronto e.g. we have raccoons that leave a present once in a while. Lots of different factors help to make your deck dirty, so there is no choice but to clean it.
If you have kids, you might be concerned about using cleaning products with harsh chemicals. For the green mind there are a couple alternatives on how to clean a deck using natural products. Check out Natural Deck Cleaning Products on the ehow website for more details.
Oh, and when it comes to raccoon feces… The best method is to pick up the present with a plastic bad, same as with a dog. Then apply boiling water to the area. Use an outdoor broom if necessary. This procedure will help eliminate odors which otherwise will have the animals come back to the same spot for their business.