When a lot or plot is graded to a higher or lower finished grade level than the natural grade, which is surface of the ground prior to excavation, filling or grading, or after a lot or plot is graded, it is a higher or lower finished grade level than the natural grade or finished grade, on an adjoining property, the owners or developers of such lot or plot shall provide suitable retaining walls or other approved protection on his property to protect the adjacent property from caving of earth and as required to maintain the existing natural grade or finished grade of such adjacent property. (Ord. 81-31. Passed 5-4-81.)