im not sure if u bought one or not.
get a GSD.
Dont chain it, you will only frustrate it. It as natural guarding instincts that can show even at age of 4 months.
get a non-pedigreed from a pre mature litter puppy that will cost you around 30-40k.
give it boiled meat after age of 3 months or some good dog food.
potty train it as soon as you get it.
train it to walk on your left side always. dont let it pull the leash when u take it on walks. if it pulls, stop and wait it for to get in settled and stable state.
discourage it to jump on you and other family members.
for guard training, make a ball of old used clothes, tie it fastly at end of stick so dog can grip that ball of clothes in his teeth.
use a long leashto hold the dog and ask a friend to tease the dog with that stick. let the dog grab and bite the cloth ball area.during this time, only teach the dog to let go on command 'NO'. this is the first and most valuable command that the dog should know when to stop and stop at first command. it can save life of an innocent human being.
if you want your dog not to eat from a strangers hand, then from pup age, give the dog food only in one steel bowl from which the dog can eat all his life. dont ever throw food on ground for it to eat. now tell a friend to give the food to dog in a different bowl and when the dog starts to eat , tease the dog with the cloth ball and stick again. the dog will never a trust a stranger with food again.
remember that the dog thinks of you and your family as its pack but it must know that you are the pack leader. some dogs bite owners or owner kids especially when the dog is eating food and u get too near because then the dog is thinking that dog is pack leader and human is subordinate to him. To ensure this never happens, show the dog his worth and low level by first letting the dog see when u eat your lunch or dinner. after u and family have finished their meals and the dog has watched u eat, then give the dog its food. in the pack the leader eats first. this way the dog gets to know you are its pack leader.
anyways i can give more tips. let me know if u need. i have kept many breeds like GSD, labs, rotties,dobes, bull terrier, bully, spitz, gaddi kutta etc and trained them.