I agree with Beret, your pup is young best to address now. I like the clicker because it keeps emotion out of your voice. My boy could pick up on emotion really easy, he also used to be QUICK to go over the threshold that was described above. Lots of subtle signals can be picked up on, but the main thing is to make sure you see any and all distractions before your dog does, so when he does see them you do not give him time to reacts or give the stink eye as I call it. Stare down, whatever it is that's not making your boy feel relaxed and able to focus on what you're asking him. Another indicator your dog is over the threshold is they will rarely take high value treats until they go back below their threshold.
The above method is known as Positive reinforcement training. here is another video about it. These are extreme cases, but you can get the jist of that the PDF detailed. https://www.youtube.com/watch?v=OMLr...-KiOojUtlInJ9w
I do not agree with everything in this video. I use a combination approach or positive and corrective, my boy did not do well when he was allowed to make his own walks as positive training allows. I do not allow him to follow and sniff after dogs, I go where I want him to go and I use a prong collar. According to this guy its punishment, I do not agree, I think every dog is different some things work and some do not its about taking the time and finding what works for you and your dog.