GARDNER — A group of local pet owners is organizing the ultimate “dog day” of summer next month. Featuring canine-related vendors, training tips and the election of a new dog "mayor", the Aug. 21 event will mark the second anniversary of the opening of the Gardner Dog Park at Pulaski Playground on Charbonneau Street. “I think the dog park has become a main attraction in Gardner,” said organizer Caitlin Hart, whose dog, Koda, has served as the first mayor of the park since its ribbon-cutting ceremony in 2019. “It really just brings people together, and I’ve met so many different people because of our dogs.”