territorial guarding

Question
we have a 3yr old pure German shepherd we installed electric fence as there is not enough room in the back yard for her and a local bylaw prohibits more than a three ft fence out front. She has developed an attitude that the front yard and SIDEWALK is hers and will will now pass through the fence and go after unfamiliar dogs.

Answer
I never recommend electric fencing with any of the herding breeds for this reason.  They were bred to herd and guard, and they tend toward barrier frustration and aggression.  Herders should, ideally, have solid fencing away from the temptations of joggers, dogs, cars, etc.  When kept like this, they just get worse and worse at the fence running until you have a real mishap.  If she is blasting through the fence, she is more willing to "get" what's on the other side than she cares about the pain in her neck (and it is pain).  

In your case, where there are prohibitions against a high fence, you are at a real disadvantage with this dog because if you continue to contain her as you are now, she is just practicing the behavior you don't want (hence she will get very good at it), and you risk her getting into a dog fight or biting a human who tries to break it up.  If this were my dog, I would put a 12 x 6 kennel in the back yard if there's room for that (and I would cover the sides with canvas or a solar cover to block her view), or I would not leave her outdoors - there are other means to exercise a dog, such as day care, fetch games, agility, or obedience training.  I know this probably isn't what you wanted to hear, but even if she only breaks out once in a while, she is in grave danger, and she might pose a danger to passersby.  In some states, it would actually be legal for a person who felt threatened by her to shoot her!  So, in my opinion, you shouldn't leave her in that area unattended, and not at all if she won't come to you immediately regardless of what's over the property line.