I want to say Horsetooth... but looking at Google maps, that seems too far south to my memory. This one was closer to Laporte, close to the Chapel Animal clinic (where we took Buddy, Dr. Soto was AMAZING) and had like a pool area for the dogs to jump in, some big boulders/trees, hiking trails outside of the fence up into the foothills... it was the nicest dog park I've ever been too. Was about 4 or 5 years ago.