I ran into a problem where a houst has a build on back patio with a tin roof. the runoff from this dug a hole all along the back edge and now it holds water after rain which gets the concrete slab wet. the back yard has excellent drainage except for right where the runoff goes. My question is beyond a gutter is there a solution to allow for the runoff but not have it hurt the landscape? I was thinking dig it out and put loose large rocks or flagstone. Extending the concrete is not an option because it will always become dirty.