Soultions for sudden dog aggression

Question
Karen,
This is not a question but to let you know that I have done several things
since
our Lab/Shepherd suddenly attacked our Chihuahua.   First, thank you for
your quick and informative replies.  I am very appreciative of your thoughts
regarding the situation.   Both dogs went to see their Vet.    The Lab got a full
work up and physical.   Everything came out normal.  The Vet believes the Lab
was upset about not being let in the house.   She believes it was a transfer
aggression issue.   She suggested we might consider a medication for the
next three to six months while we retrain him.    The trainer does not think it's
a good idea.

The Chihuahua got his staples out yesterday after ten days and both dogs are
making nice.   The Lab is wearing his muzzle off and on.   

Tomorrow we start training the Lab with a highly recommended trainer.   He
trains police dogs for neighboring cities.
We (the dog and my husband and me) met the trainer at his facility for about
two hours last week.   He believes with some changes we can live happily  ever
after.
We are encouraged and optimistic that family harmony can return to our
peaceful cottage.
We have made immediate changes in not allowing the Lab on the sofa or
continue to bark after we have commanded him to stop.
So this is all the news.
I wanted to share it with you.
You were very helpful.
PM

Answer
While I don't agree that the transfer aggression was due to the dog being left outside, I do feel that it had to do with his fear of being introduced to the stranger and your correction of him. We sort of said the same thing, but with different causes. Same difference in the end, I guess.

If medication tones him down enough so that he can become "sane" enough to work with, I don't see anything wrong with that. When a dog is too stressed or fearful, it is very hard to communicate with him and training does nothing.

Good luck with the new trainer! He sounds very promising. Just remember that whatever changes are needed will be for a lifetime not just for a few months.