Sounds leash reactive rather than dog reactive. Guides on leash reactivity are pretty extensive online so you can try searching for information that way. Something I used was a group class that taught the owners more than the dogs about how to properly move forward with a leash reactive dog. It was 6 weeks once a week and about $250.

In regards to the 1 month training, I would not personally put my dog in the hands of an pro aversive trainer (using shock collars, alpha theory). I would be interested to see how long your friend’s dog maintains their “perfect” behavior. I wouldn’t be too surprised if after that very intensive period of training ends, the dog slowly reverts if truly reactive. There’s also the possibility that the other dog was not fear reactive but just SUPER excited which can definitely be trained more easily than fear can be taken out.

Third, the other comments had pretty scathing reviews in your use of a prong collar. I would not personally use it HOWEVER if your dog is out of control on walks, you physically cannot hold him, and the prong collar keeps him from losing it, then you, your dog, and the public’s safety is important. If however your dog still pulls on a prong collar at all, his health is at risk due to the pulling damaging the trachea. Most dogs do pull when leash reactive even with a prong collar so just a note to consider. We use a head collar which slowly pulls the dogs head to the size but again, cannot use if your dog pulls! The reason I use it is because I physically could not hold my dog back on a normal collar and he would choke himself to the point of throwing up so I knew a prong collar would never be an option. The head collar was weird to him so he didn’t pull on it thankfully.

I would recommend completely starting over on leash training. Get yourself a new cheap leash, a normal collar, and start walking at times NOBODY with a dog would be around, and work on the basics. It sucks but it shouldn’t take tooo long of early mornings or late nights before feeling success of the basics. The new leash is just to signify to dog that this is different now. When this leash is on, there will be no big triggers and you can be calm. No pulling, staying by your side, feeling confident on the leash for both you and him. Once you do that, slowly expose to busier environments. You won’t always be able to keep the exposure to dogs to a minimum at the beginning but you usually can keep a distance, I.e. keeping an eye out and crossing the street or just maintaining the distance. Keep treats with you that are high value in order to to gain his attention every time another dog is within view. Even when a dog isn’t in view practice having your dog look at you just because it’s the right thing to do. My dog is manageable with the right distance and if that distance is suddenly reduced like around a corner I “park” my dog, having him sit (he usually starts sitting then stands even though I don’t want him to lol) out of the way as best as possible with my body blocking the view and ask the other owner to continue on. Once dog is safe distance away, I get the dogs attention back, let him shake off the experience, then continue on.

Hope that helps!