I have a small backyard that ends off with a steep slope which leads to some sort of sewer / creek at the bottom. I have already gotten a wooden wall built behind my porch, which is now separating from the foundation of the house. Apparently that wooden wall wasn't enough and now the dirt next to the wall is starting to wash away into the ditch. I'm thinking about putting up a retaining rock wall but then, I am also concerned if the retaining rock wall will be washed down into the ditch after a couple of rain showers. What should I do about this problem before my entire house washes away?