new dog with old

Question
We just rescued a 1 year old male Jack Russell.  We already have an 8 yr old female Portuguese Water dog who was more than willing to accept him.  However, we have had several instances when the Jack Russell (Leo) has started a fight because he wanted to be the "leader".  My Portie is now not too happy, very timid and keeps her distance.  They can spend time together in the car and outside without any problems, he even seems to follow her lead, but then... I correct Leo immediately when a fight starts and notice that he is still growling under his breathe even though I am telling him that it is not acceptable.  Finally, my question, will my Portie be permanently tramatized and is this just a transitional period that will end if I continue to correct this behavior.  I read your other entries and Leo definitey knows "I" am the Leader - he is great, smart and seems to always "get" it - but then again.. Leo has just recently arrived.  I feel like Nellie would like to be friends and things seemed to be getting better when all o a sudden Leo popped!!!  I appreciate whatever info you can give me.  Thanks.

Answer
Hi Deborah,

That was good of you to adopt the Jack, and I'm sorry you're having trouble with the adjustment period. It sounds like you're doing everything that you're supposed to be doing - and to correct the behavior immediately is key. Actually, if you can correct it at the first sign of aggression, the better... like if he looks at her the wrong way, give the correction - if he raises his lip, make the correction, if he growls, make the correction.... try NOT to let it escalate to a fight, but I know sometimes that happens. You'll just have to watch them very closely for a while.
Whenever there are two dogs in ANY household, one will always take the dominant role. It's crucial that YOU are the pack leader and keep things in control (which you are).  Make sure you don't get nervous or "hysterical" (for lack of a better word), by yelling in a high pitched voice, etc. Make the correction swift and use minimal language. "Stop" "NO" or a sound like the "pssh" and a firm touch on the neck.  As Cesar Milan says, stay calm and assertive. Don't let him know you're nervous in the least.
Try your best and stay consistent. It's going to take a while, probably a good few months, but keep the course!
There have been cases where the two dogs just couldn't get along but that is usually with an older dog coming into the house. Leo is still young enough that you can do great work with him. Training and consistency works wonders. Good luck to all of you!