2 females

Question
we have had a 5 year old airedale for 1 year. she is a rescue dog. Our 24 yoear old son just got a 4 year old female. Whenever they get together, even on neutral ground, they our dog gets this low deep ominous growl. How can we get them to be friends?

Answer
Try bringing them to neutral ground such as a park or beach and see if the response is less aggressive.  Sometimes when a new dog is brought into an established home the older dog will be very dominant to establish itself as higher in the pack order.  When meeting on neutral ground the instinct to protect the territory can be diminished.  I would walk them together (you and your son) and do not acknowledge the negative behavior-allow the built up energy to be transferred into forward motion.

It may take a while for the older female to accept the younger, and will be by your example.  By your treating them both as members at the same level in the hierarchy, you should see a change in the older.  If the situation does not improve, I would recommend calling a behaviorist in to help you with body language and behavior modification techniques.  When choosing this person, be sure to work with someone experienced in actual behavioral issues, as that is different than a "trainer" and also choose one that uses mainly positive techniques.  Corrections may be necessary, but should not be the entire focus of your work with the dog-you should see great achievements using positive training methods.  Compulsion, or do it because I said so type of techniques may control a behavior in the short term, but generally cause a much more aggressive situation and the first time that control is not in place, what would have been a heated discussion could end up being a serious dog fight.

I wish I could help you more on this, but in these situations I would be lax in trying to completely help you via online questions.  the key to this issue is going to be perfecting your timing and ability to read body language.