This story was produced in partnership with FuturePerfect, www.resilience.org/stories/2015-06-08/art-that-walks-in-the-world#   Daniel McCormick and Mary O’Brien have received plenty of accolades for their public sculptures over the years. But the review they like best? The turtle scat that they discovered each morning along one section of their work. “The animals found it instantly and that made us feel really good”, says O’Brien, referring to a 270-foot-long piece they built last spring along the Carson River in Nevada with the help of hundreds of volunteers.  Animal droppings probably wouldn’t excite most artists, but McCormick and O’Brien specialize in creating sculptures whose purpose is to help heal the environment. Their “Watershed Art” has appeared in the for...