I have a 6-year-old Yorkie and her 3 pups, now 12 months old, who are all in the habit of barking at any sound they hear while out in the garden. If only one of them hears it, the others join in anyway. Passing sirens are a special trigger. Now neighbours are complaining and threatening legal action. How can I improve matters? I know Yorkies like to make themselves heard, and have tried to calm them down, to no avail. Help welcomed!