we have a ranch in long island ny and our house is downhill on a slopy street. our backyard is therefore downhill but I do have it all flat in the back. due to soil erosion, I have a gap between the land and the fence on the left side of the backyard if I am facing it. the slope is deepest in the left corner I would say 3-4 ft which makes us unable to use it and there is not much landscaping there either. what is the solution. is retaining wall the only answer or can I fill the gap with dirt and plant shrubs. I was told by few people its going to push my fence down with the pressure of the dirt. pls help!!