One of the most important aspects of permaculture design is edge. Edge is a fascinating point that is located between to different environments such as forest and glade. One of the difficulties that can arise in a permaculture site is the maintenance of edge. Typically the designer will know exactly where each and every edge belongs and what type of maintenance is required if any, but assistants and volunteers may not be so certain. In the linked video Tom Kendall discusses the importance of marking edge and its roll in aiding edge maintenance.

http://permaculturenews.org/2015/06/26/the-importance-of-a-defined-edge/