This came up in another thread, so to avoid taking that one off topic, I'll put this here. To train a whistle, first you have to teach the dog that it is an awesome thing, then by default coming back to you is an awesome thing. So first, charge the whistle (I recommend an acme whistle, easy to replace with the same tone if it gets lost). Simultaneously - that's important - pip the whistle and feed a piece of roast chicken or frankfurter sausage. Do that five times in succession. Repeat that five times in the day (so 5 x 5). Now your dog knows whistle = sausage. Do that over several days. Then take the whistle to another room. When you whistle, your dog should be running for his reward. If not go back to the previous step - which is always what you do if a training response fails. Practice in the house for a couple of days and then take it to the garden. Once he is solid in the garden, use it in a low distraction environment outside. There are, in my view, three main reasons why a dog doesn't do as you ask. The first is he doesn't understand - so your work in the house to train to this point eliminates that one. The second is that you are fighting a deeply rooted breed trait - there is a reason why we don't use terriers to herd sheep. It can be trained but it's a lot harder. It's the third one that's potentially an issue and that is that the reward or motivation to do what you ask is not as high as the reward or motivation to keep doing as he is doing. So if he is having a ball, chasing squirrels or playing with other dogs, a piece of sausage may not trump that. So, don't set him up to fail by whistling when you think he us unlikely to come back - practice, practice, practice in low distraction situations until he doesn't even think about it. Very gradually try a whistle with a distraction in the distance and eventually, decreasing the distance, you can build up to recalling being solid no matter what. And during training, if you think there is a risk he may not recall, use a long line (only ever attached to a harness, never a collar to prevent neck injury) so he cannot fail. After a few weeks you can fade the reward. Sometimes sausage, sometimes normal food, sometimes an ear rub. By mixing it up, you will keep his interest - the ”what will it be” factor. Its apparently the same reason why people play slot machines.