My name is ***** ***** I’ve been involved professionally with dogs in the health and behavioral fields for over 18 years. It will be my pleasure to work with you today.
Dogs become sexually mature around 6-7 months of age, but it is closer to 18 months before they feel more like an adult and develop adult behavior. You often see changes to behavior around this age as they are starting to become adults and feel it may be their job to protect their "pack" (you) from strange people and things.
There are things you can do to establish yourself as the boss and thus the protector of the pack. You can step up his obedience training so that he listens the first time every time regardless of distractions. The following site is helpful in helping owners train their dog. Be sure and click on the link to the page on obedience at the bottom. and links on subsequent pages leading to detailed instructions.
Training works best if you train at least 30 minutes a day (two 15 minute sessions). I would start making your dog work via the Nothing in life is free program (NILF). It is outlined below.
Once you have some of this type training done and have him listening with distactions better, you will want to introduce the very things that set him off. This will require you to enlist some helpers that are not the norm for the people he normally sees. What you will do is have them walk past in the distance while your dog on the leash. You will have your helper off in the distance. Your helper will gradually move a bit closer to you preferably walking past your position in the distance. As long as your dog ignores them, you can give your dog praise and a treat (hot dog slivers work best). The second you see him fixate on the other dog or show any other sign of aggression (hair standing up, etc.) give your dog a correction by giving a short tug and a firm low toned "NO". It shouldn't take your dog long to realize you will not tolerate the aggression and that if he ignores the person, he gets treats. Once this happens you can repeat the training moving the helper closer until he is no longer trying to bark at the helpers. You will need to practice this when you and your dog are walking as well.
Once she is no longer barking at that particular type of person, then have the person themselves toss your dog some tasty treats so he associates the unusual people with getting tasty treats. Then move onto a different type of person that he reacts to and restart the training. It should go must faster this time. Repeat as needed for any unusual situations where he barks or displays aggressive type behavior. This training helps with aggressive barking as well as fear barking and helps desensitize him to various other types of people. Puppies adapt quickly so usually it is best to introduce puppies to various groups of people including children, the ederly, other ethnic groups and the disabled so they don't view these groups as unusual and treat them like they do anyone else.
A bark collar may help because it will deliver an immediate reprimand in the form of a citronella spray or shock at the first sign of excessive barking which may help with the initial training. I would only use it while the helper is in the distance so he does not associate any reprimand with the person.
I hope this information is helpful to you. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have . If you do find this helpful, please take this opportunity to rate my answer positively so I am compensated for my time. Rating will not end our conversation.