I try to socialise Brian safely safely, so:
I make sure Brian’s got an escape route (so when he’s scared, he can move away, preferably to me)
If he uses the escape route all the time, it’s better to move away permanently (the other dog might be a bit too much of a challenge)
I make sure Brian still comes back when called, to keep the balance between satisfying his curiosity/ the need to play and his safety (I do consider recall a safety command)
I never use treats as an enticement. They can be used as a reward but he shouldn’t come because he wants a treat. He should come because he’s conditioned to do it.
I avoid people and dogs who seem to want to avoid us. Whatever the reason, I need to respect their right to be left alone.
We try to play with puppies who are similar age -fortunately we know quite a few. With older dogs, I would intervene if I saw that the older dog doesn’t want to play at all.
I add challenges gradually, with a lot of space for Brian to retreat to. When we meet strange dogs and they want to play, I don’t supervise actively, just watch, making sure my body language doesn’t signal any concern or fear.
Every new experience MUST end in something positive. So, if anything goes wrong (it’s mostly people, not dogs who make socialising difficult, actually), I’d play with Brian (tug of war works for him) as if nothing’s happened. He knows that even if sniffing a dog’s bum has resulted in the owner shouting and panicking, it’s still mostly ok to sniff dogs bums, because 1. most dogs are ok with it and they’ll play 2. if not, life is still full of fun.