Simple-looking problems, Bob McDonald knows, sometimes have complicated solutions. This is why the 12-foot-high retaining wall in front of his house at 3127 Adams Mill Road NW is still lying in a jumble of rocks, rubble, and earth at the edge of the sidewalk. The stone wall tumbled in March 2000, and a city engineer says an adjacent section could follow. Though the wall sits on public property, it’s the homeowner’s job to fix it. The question is, how? The project is too massive for a residential contractor and is chicken feed for a major construction company. And whoever does the job has to somehow keep the ground under the house from slipping while working in the narrow staging area of the sidewalk. McDonald reports better luck finding an engineer: “He normally does commercial work, but he took me on more or less because of sympathy,” he says. —Joe Dempsey