The Fear Phases

             Dream Tip + Bip. Training + Behaviour. The 'FEAR Phases'.
It is widely accepted that young pups and dogs can go through a number of phases relating to anxiety or fear. These can be around 8 weeks, 8-10 months (teenage hormones) and again around 18-20 months the maturing phase. The stages are related to, hormones, exposure to stimulus and socialisation.
You may think "where has my happy puppy gone?"
He is reacting, by barking and lunging, feeling he has to take control of what he sees as a potential threat / stimulus situation.
It is crucial at these times to, remain calm, go back to basics with your dog, and be aware of, and acknowledge his alerting you, and the emotions he is feeling.
On a walk, you need to read the road ahead, you may have to stand back from the things your dog is reacting to, humans, dogs or traffic, at a safe threshold, to desensitise, keeping his attention on you, rewarding when he engages back with you. Let the dog make his own mind up about meeting people, don't push it.
Be a firm leader, especially around the 3 areas of control where your dog thinks he is the boss... that is food, toys and doorways. Always ask your dog to give you something, before you give him anything, this could be a wait, sit, paw, or down.
With positive, careful, management, your dog should move through this phase, more mature and able to cope with the big wide world.