Don't listen to 'em. I believe as you do that air flow has a lot to do with it as in most cases back yards have fences or hedges surrounding them with the house as well. Stagnant air= moldy/lichens/moss, since it won't dry out as fast where the wind blows more freely. More humididity (Llyod Lindsay Young, channel 9, remember that guy? Helllllllooooooooooo Bobby G!