How do I get my dog to stop mouthing / jumping up / nipping at heels ?

Hi Patty! My dog was doing exactly the same, and we had doggy training classes. We were taught exactly the same - to turn your back and ignore the dog if they were jumping up, plus a firm "No" at the same time. Your Shih Tzu is only 1.5, so is still growing up and going through his puppy stage. Persevere with what you are doing, and make sure your friends do the same because it does work! One day all of a sudden they DO get it, and magically stop! It's just because he is so exciteable being a puppy. Most dogs are "grown up" by 2, and they just get nicer and nicer after that :-)