We’ve had him for 5 years and he’s as good as gold apart from the minute he hears the next door neighbours’ grandchildren arrive (with or without their dog). If he’s already outside he barks and barks, tail up and wagging mostly. But he doesn’t stop. The kids are little and noisily playing. He can’t see them but obviously hears them. He does the same if the dog is out too. He barks constantly and there’s no shutting him up unless I get him to come inside and ensure he can’t go out again. In winter this isn’t too problematic but in summer this is impossible. What can I do?