Where the subdivision contains park areas, road maintenance systems or other facilities or services which are necessary to or desirable for the area, and which are of common use or benefit and which are not accepted for maintenance by an existing public agency, provisions shall be made by trust agreement for the proper and continuous maintenance and supervision of such facilities. A final and signed copy of said agreement shall be attached to each and every plat having a facility or service covered by such an agreement. (2005 Code)