GSD with 2 other small dogs

Question
My wife and I have 2 Cairn terriers, ages 5 and 1
The 5 year old is a nervous type but the 1 yr old is fearless...but friendly/playful
I was contemplating getting a German Shepherd.
I work in a job that I go into properties all hours of the night and have heard they are the perfect dog for my personal companion/protection.
My question is will a GSD get along with my 2 Cairns.
Than You

Answer
Much of it depends on your leadership.  I have a friend that has Cairns and has had several Shepherds.  She is a very strong leader, not harsh, but very much in charge in a positive way.  The key to most behavior problems is approaching things using the dog's natural instincts.  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

Many Shepherds actually are sort of wimps, but most people that might be up to no good, just don't want to confront one.  You will be better off teaching it to be friendly to strangers just allowing its presence do most of the work.  Actually dogs are very good at judging people and will react appropriately when they need to.