But he has grown up and started to get dominant with the Lab, who has been
the undisputed boss until now.

   Can you crate the younger with lots of chew toys at night in a place the
alpha isn't allowed?

  I had a lab who used to be the youngest of four dogs. She was picked on by
the alpha dog until she got old enough to assert herself, and then she
mauled the alpha one day (the vet was only a block away so the alpha was
saved, but barely).
  I'd wonder why your dog seems so scared; he has no escape from the other
dogs he lives with and that could be triggering this.

Rini
No virus found in this outgoing message.
Checked by AVG.
Version: 7.5.519 / Virus Database: 269.22.10/1367 - Release Date: 4/9/2008
7:10 AM