An ornamental wall, fence or screen planting acceptable to the planning department, and no less than six feet in height shall be erected and maintained along the side and rear boundaries of a mobile home park. Where, in the opinion of the planning commission, it is unreasonable to require a wall, fence or screen planting due to the nature of the existing topography or other existing conditions that might render such wall or fence ineffective, the commission, at its discretion, may waive or modify the requirements as specified in this section. (Prior code § 17.68.010.)