My house has a walk out basement in the middle back. The ground slopes sharply down from the sides to this point. To one of the side of the walkout I have a deck which ranges from 3' to 8' high as it approaches the walk-out. Rain water falls thru the cracks b/n the 5/4" boards and washes the dirt downhill. I have a series of troughs now, one under each crack, some as deep as 6". What type of cover should have been placed over the ground under this deck? (e.g., gravel, landscaping fabric, both)