The leash sounds like a good idea, maybe try adding leave it, enough commands. Our dogs used to bark or go to the door when a doorbell rang on tv, but just perked ears if it was an dog barking/howling on tv. We'd say "it's the tv" and after a while they learned the difference between the real thing and tv! Like said I imagine others will have ideas! Commands such as you might use outside around other animals or when you have visitors.