Hi elmac,
Apologies for the delay!
Well, I started off with distraction techniques for Eddy, literally, as we passed another dog, something good always happened - he got some food, or a fuss etc (he doesn't play so that made it a bit more awkward but a game of tug would've possibly worked too - you just have to be careful you don't gee him up too much!).
Then, as we saw another dog, we'd move off the path slightly and Eddy would have to sit, or do a trick or something and as he did so he got a reward.
If he paid attention to the other dog and I lost his focus, I called him in a happy voice, walked him around in a circle until he was looking at me and then 'Yay! good boy!' for focussing on me. He's very food motivated so this was good for him as he got a treat when he was focussing on me.
(For smaller dogs, a 'touch' exercise is good if you have an extending touch stick so you don't have to keep bending down).
Gradually he came to realise that quiet is more rewarding so would just eyeball the dog instead, by this point we could move onto shaping less interest in other dogs and more interest in me. Note that my main aim was to get him to ignore other dogs, not that I particularly wanted him to be able to interact with other dogs as I didn't think it was really possible at his age and felt that as long as he wasn't attacking, it would be ok.
The key is timing. I had to get his attention before he focussed on the other dog, and I had to reward at the right time so I wasn't reinforcing his negative interaction with other dogs.
I used an extending lead so he could always have a run but I could reel him in when another dog was nearby (this can cause your dog to associate the dog with his lack of freedom though so the key is to attempt a recall first and then make yourself as exciting as possible whilst pulling him out of the situation!).
When he was able to walk by dogs at a distance and focus on me, I gradually decreased the distance between the dogs (always putting myself in the way) so that he could get used to passing closer and for each positive encounter he was rewarded the moment he looked at the dog quietly, or looked at me.
Any negative interactions were always ignored. I was in control whilst he was on his lead so I didn't say anything so that no negative associations were made and I certainly wouldn't join in with the noise!
Eventually, he was at a stage where I felt he could begin meeting dogs and realising they weren't dangerous.
I took him out on his extendable and got him used to wearing a muzzle. I was quite confident that he wouldn't harm another dog but I hadn't had him
that long and it was more for peace of mind. I asked people with friendly dogs if I could introduce him whilst on his extending lead so I made it long and tried to distance myself from him so he didn't feel too claustrophic, he had the muzzle on so there was no fear of attack. As soon as I noticed a peak in discomfort he was removed from the situation because I didn't want him to try the attack (because the possibility of him blowing up at another dog would increase the possibility of a repeat event later on).
I had to really learn to shut my mouth with Eddy. If I said anything it was a very quiet coaxing 'good boy' while he was doing well but if he did start to growl or bark I made no sound, just moved him away. I realised that my own voice was carrying some degree of tension whether I liked it or not and the more noise I made (particularly when he did blow up) was making the situation worse.
I
never say as I've heard some people say 'be nice' in that low growly tone that basically says 'that dog is something to be worried about'.
To my amazement, at 12 years old, Eddy now walks off the lead, saying hello to other dogs (and then coming to me for a treat) or playing with them, he occassionally gets offended with small dogs and I recently learnt he has had problems with a JRT before (and was attacked by a border terrier half way through his resocialisation with me) but in general, he's much better.
The main problem with this sort of behaviour is it is self reinforcing, the dog attacks/barks/whatever and the other dog runs away.
If you can meet with someone who's dog is not fussed and will not run away it will really help.
I'm sorry I know that is really, really badly explained but I hope you can gleam something from it!
My only other pieces of advice are:
Only introduce him to other dogs if you're confident he's got to a stage where he's not too likely to blow up at the other dog and don't put a muzzle on him unless he really is comfortable with it otherwise it could certainly make it worse (both flight and fight options are taken away and he could associate it with the other dog).
And...
There is a very good book called Click to Calm which I acquired after resocialising Eddy and basically explains the methods I used far better along with other ideas!