3rd dog

Question
Hi, I own a 1 yrold JRT neutered and a 9mo old female Rottweiler spayed. If I was to at some point introduce a 3rd dog, what would be the best breed type to coexist with my two existing ones, and what sex would go best with a male and famale.....yeah, the whole 3rd wheel thing i know, 3's a crowd etc. I would prfer a happy medium, so a medium sized breed/ mixbreed as opposed to a toy breed...I exercise them 2 hrs a day, so although my living space is not very large, they usually just loaf around inside or jaw to jaw play with eachother......they are very close as only 6mos apart.....so the age of a 3rd dog in varience older or younger would also be a factor.....a more submissive breed as the Rottie is more calm and another calm breed would probably only help the sometimes exhuberant JRT.

Answer
I am not going to make any breed recommendations.  Your Rottweiler may be submissive, but I am not sure other members of the breed are.  I see many Labs, and although some things are common, in other ways, they have been very different.  I see the same thing in other breeds too.  As far as getting along with other dogs goes, I think the biggest factor is pack rank within a litter.  Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog.  Life is much easier if the 2 legged pack members outrank the 4 legged ones.  You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at http://www.dogsbestfriend.com/  For more on being top dog, see http://www.dogbreedinfo.com./topdogrules.htm  

Each litter arranges itself with a top male and a top female and the rest of that sex following in a definite order.  The worst possible case is the dominate females from 2 different litters.  You best bet for 3 dogs is 2 males and one female, making sure the new male wasn't the dominant one from his litter.