Existing fences. A fence lawfully in existence as of the effective date of this article which shall be made nonconforming by this article may be continued except as otherwise provided herein. No fence which is nonconforming shall be changed, enlarged, extended or reconstructed except to a conforming fence, but no provision hereof shall prohibit the repainting, staining, waterproofing, minor repair or insubstantial alteration of an existing fence. Any nonconforming fence which is destroyed less than 50% by fire, other casualty or act of God may be repaired and used in the same manner as prior thereto, provided that the fence is not enlarged, extended or otherwise materially changed. All such repairs shall be completed within six months after the date of partial destruction or the nonconforming fence shall be deemed to have been abandoned. When destruction of a nonconforming fence exceeds 50%, the same shall not be rebuilt or restored except in conformity with the requirements of this article.