Woofy whilst I usually agree with your advice regarding animals you are contradicting what I was told when consulting a dog psychologist about this behaviour from my own dog. She said the worst thing you can do, and so many people do it, is to take your dog away from other dogs. You should do the opposite and take them where there are plenty of other dogs or they will never get used to not reacting. Fruitsalad's dog is exhibiting fear aggression, ie yap yap bark bark clear off please. You won't stop him over night and you will have to be persistent. It is not dominance aggression or he would go in for the kill, climbing on top of the other dog to show who is boss and possibly actually biting if resisted.
You must distract him before he reacts by giving a small treat in the beginning, then after a while calling him back and making a fuss as an alternative to treats etc.
This link might help, the first bit anyway.
https://www.wikihow.pet/Stop-a-Dog-Barking-at-Other-Dogs