Whenever three (3) or more townships shall have been formed into a unit for the purpose of restraining any stock as enumerated in § 14-387-301 and shall have been perfected in the way and manner as provided in this chapter, then any other township, or any group of townships, that would be a contiguous whole to the unit thus formed, may be attached to, and become a part of, the unit, in the same way and manner as provided for in this chapter in the first instance, by merely stating in the petition, in addition to the other requirements, that the petitioners wish their township attached to the unit, naming the townships in it.