All training, whether clicker or conventional, tends to work a lot better in the living room than on the training field.  The reason for this is that new and exciting out-of-door environments offer a lot of external reinforcers to dogs.  Basically, they just get distracted, and proofing, or teaching the dog to continue to work with distractions around, is an essential part of every exercise.  The presence of other dogs can be a particularly difficult distraction to overcome, but there is at least one surprisingly simple and fast approach to solving this problem.  The article contains a couple of video clips so is best read via a fast connection.