GSD - Wiered behaviour

Question
My GSD (Cissor) is 15 months old. We bought him as a puppy for gaurding our farm. He is never alert even towards strange people.. But he gets crazy and barks continuously if he sees other animals; Cattles, dogs, sheeps etc.. He tries to always play with familier people by trying to bite with his sharp teeth. Becasue of these unexpected behaviour my father is upset at him.. Father wants him to be good gaurd dog against stange people. If Cissor stays same then I fear my father would send him off..
Is there anything to change him. He should be alert and aggressive towards non-family people.. Plzzzzzz help me.. I don't want to loose Cissor..!!!

Answer
Hi, Sidram,

Your dog is in his adolescent time, so his biting is a form of playfulness, which is normal for a young, happy, healthy dog.

German Shepherds were bred to herd animals, which would explain his interest in sheep and other animals.

The description of the breed, from the American Kennel Club, states:
" For his typical work as a herding sheepdog, he must not be gun-shy and must have courage to protect his flock from attacks, either animal or human. For his work as a police dog, a development which followed upon his natural aptitude for training, he must have this courage and in addition must be able to make use of the excellent nose which he usually possesses. In his work as a leader of the blind, the Shepherd must and does exhibit a high order of intelligence and discrimination involving the qualities of observation, patience, faithful watchfulness, and even, to a certain degree, the exercise of judgment."

If your father wants Cissor to be a guard dog, he will need to have the dog specifically trained for this.  German Shepherds have a natural aptitude for being protection dogs, but they need to be taught HOW to do it.  I don't think being aggressive is a good idea, because where I live if a dog attacks a person, the owner of the dog is legally responsible.  I don't know if this is the same where you live.  There is a form of training called Schutzhund, similar to what law enforcement officials use for their dogs.  I don't know how much this costs where you are.