Originally posted by Kfamr
The thing about it though, I barely touched Duke. BARELY at all.. and he snapped twice at me. It scared me a lot. I think the factors in him snapping at me were: 1.) He was by his mom. 2.) He was on the couch.

I really don't like the idea of letting them "work it out" - with Nala i'm pretty sure one of them would end up getting hurt. I wouldn't be able to forgive myself, Duke, or Nala if either of them got hurt. With Kiara, she's not willing to "fight back" and Duke has "put her in her place" many of times, all she does is cower down or try to get away from him.
More information = more pieces of the puzzle put together! I would still have Duke checked for possible pain. The rest of this is with the assumption no medical issues exist.

Being by his mom is no excuse. Being on the couch is no excuse. How did both of you handle this situation when it occurred? Especially Valerie!

I can see the point in not letting them work it out since they are not together all the time and this would be an ongoing issue everytime they get together again. I personally would not separate them. I would just keep them on a leash so quick corrections could be make if things become heated. Separating them can cause Duke to feel like he "won" if Kays are separated and can cause him to be more aggressive if he is separated. Keep them together but in a very controlled environment. Kay, I am more familiar with you around dogs than Valerie so I know you can do this! It is important to establish humans as alpha over all the dogs.

Letting Duke know this is unexceptable behavior and giving him a consequence when it happens is vital. I would probably put him on a Down stay (a submissive position) for a substantial period of time while he can see the other dogs having fun. No couch... the hard floor! Ignore him for any whining or sympathy he may do or want in the down. My only recognition would be to reinforce the down if necessary.

I would also be quick to recognize any acceptable behavior and reward him appropriately around the other dogs. He needs to learn commands that reinforce good behavior and penalize bad behavior.

Valerie, in addition to the above question, has Duke ever displayed this behavior in his younger years? Was he properly socialized with other dogs? Is he ever around other dogs other than Kay's dogs? How does he act then if he is? Does Duke see himself as the alpha in your house (including Alpha over you)?

Let's start here and then see what we can come up with.