What about trying a "throw can" -- an empty pop can with a few pennies in it and the opening closed over with tape? When the pup starts to nip, simply shake the can once (you don't throw it!) to make a loud noise as you firmly say "No!"
I've found the throw can has really helped me control my pup's unstoppable barking in the evenings whenever he heard a noise. I needed to use it only a couple of times before he got the message.
Linda |