It is possible. But it takes ALOT of work, commitment, and dedication.
Usually the dog either has it or they don't. If they have "it" you'll spend the majority of the time incorporating obedience and control work, proofing the dog, and generalizing.
With that said, just having a GSD will deter 99% of would be criminals. Remember, you don't have to outrun the bear, just the person running next to you. It sounds mean, but it's true - given the choice, criminals will choose the house without a dog, or the house with a small dog, before they choose the house with the GSD barking @ the other side.
Yes - there are "experiments" and people saying that an untrained dog may not defend you when the need arises. I believe that most criminals are not going to try and find out unless they are targeting you personally.
So, IMO your path of least resistance, and thus the easiest is to get a GSD and spend as much time as possible socializing him, introducing him to people, getting him nice and confident, and obedient. Don't make enemies if you don't have to and then get a gun if you really need to feel safe.
Last edited by ayoitzrimz; 01-30-2014 at 12:53 PM.