This is my response to the PM that you sent me...
First, this breed was never created to be property guarders. They were crated to be a personal protector - that is to stay with thie people and protect their people. I know many dobes who will try and protect their owner/person if somebody shady approaches them but, if home alone and somebody breaks in, they won't always do much. Again, this breed was never meant to be a guard dog in the way you seem to be describing.
Second, your dog is FAR TOO YOUNG for what you're expecting of him. He's still a baby! Most dogs don't start showing protective behavior until they are about two years old.
Last, the doberman is not supposed to be aggressive to everybody. That is super dangerous. If your dog bites an innocent person chances are he will be put down (killed, euthanize, put to sleep) right away. You need to socialize your dog with lots of people and other dogs. He needs to meet a ton of people (even strangers). Dobermans are intelligent dogs. They're not supposed to be aggressive to everybody but, instead, they are supposed to evaluate a person and judge whether they are a threat or not and a dog cannot do that correctly unless they meet another person and learn the "feeling" that people with good intentions give off.
My doberman, for example, is now 19 months old. He has met A TON of people and while he isn't super friendly like a lab or a golden retriever, he also isn't aggressive. He is great in public and wonderful around kids. Every so often, however, he'll meet somebody who he doesn't like. These are usually people who approach me and him when nobody else is around and they seem to give off a weird, almost dangerous vibe. At that point, my doberman gets a little protective (because it doesn't take much for him to deter people). Had he not met A LOT of people he'd never be able to do this.
Again, dobermans are not guard dogs and you're setting your dog up to get hurt whether it's by someone breaking into your house (because these people will beat or even kill dogs) or it by him being put down for attacking an innocent person. If you really want to protect your house you should get a gun or an alarm system. If you don't want your doberman for anything more than a guard dog perhaps you should rehome him to somebody who wants a loyal companion.
If you have the time, read these links. They're full of GREAT information about this breed and I think the reading would greatly benefit you.
Doberman Pinscher Club of America - Home Page
DobermanTalk - A Doberman Forum