At the time of the final site plan or plat review, the developer and City shall agree upon the appropriate restrictions to be placed on the use of that area designated as conservation easement within the planned unit development to provide for the preservation of woodlands and protection of the extreme topography within said area. The owner, developer, their heirs, successors and assigns shall agree to preserve the tree cover, not disturb ground cover within the conservation easement in a manner which will effect the stability of the areas extreme slopes, and not permit any construction, placement or erection of buildings or structures within the conservation easement area, provided decks or patios may encroach into the easement area a maximum of twenty feet (20'), if said decks or patios are so constructed and placed maintaining slope stability and preservation of tree cover. (Ord. 919, 5-29-1990)