Under a aggressive dog there's a very calm dog!

So my boy has attacked in total 4 dogs, once that was my fault and the rest where it was the other people's fault for not listening to me when I tell them to put their dogs on the lead as mine would bite their dog as soon as it comes close.

But under this insecure boy is a very calm dog and he's an example of a dog, I've started to realise how good he is and how calm he is since we've got Sasha she's nearly one and she's still a puppy but I got my boy when he was 1 year old too and he's always been very calm with people and playing.

When my boy plays with Sasha she bites him, she jumps in him she knocks him down and he doesn't care he walks away and runs away instead of turning aggressive, I thought at the start if she annoyed him first thing he would do would be bite her, since he's aggressive.

I think and this is where I need someone who knows about this stuff to help me out, every time he's attacked a dog is because the dog comes running up to him so "coming into his space", there for causing him to be scared and attack. He's been ok with only 2 dogs, and the first time they met my step dad got the other dog turned it around and got Dragon to sniff their bum, that's how dogs say hello, right? Can they tell by sniffing the other dogs bum that they're friendly or something like that?

Every single dog that he's attacked he didn't sniff their bum he just went head to head with them and then started growling, but the 2 dogs he's ever been ok with and able to play he sniffed their bum and right after that, his tail would go up (it was tucked in before) and started waging.
Could it be that he needs to sniff their bums to not be aggressive towards that dog? Because under all this aggression there's a softy who loves to play and is very laid back.

Sadly some dogs are just unsocialble. I had a Patterdale before Logan and she would have attacked pretty much anything. She was petrified of other dogs and instantly went into defensive mode, she was as hard as nails though and when she got in bother it was normally quite nasty.

Logan does not like big dogs as he has been attacked before. He hasn't biten anyone or anything but if he was able to he probably would fight with a big dog. He is growing out of it though.

If you imagine how un natural it is for to animals to meet head on the way we do on walks it can be a bit easier to except I find.

All you can do is try to socialise as much as possible when you can, but always avoid the situations when you know there will be problems

I think it's how they say hello simply because they can learn a lot about the other dog that way, but if Dragon's aggression to dogs is out of fear, maybe it makes him a lot calmer, because instead of this dog running up to him, there's a dog facing the other way while he sniffs it. Must help him not feel scared because it's not this sudden thing, maybe?

It sounds like Dragon may have been a bit fearful of other dogs to begin with, having his tail tucked under would be an example of this.

Have you seen the link below for dogs body language ? Have a quick read through it may shed some light on what is happening with Dragon:

http://staffy-bull-terrier.com/dog_body_language

Yes I've read it and I know how to tell how he is with his body language he is scared of dogs which causes him to attack.
That's why I was wondering if him sniffing other dogs is what causes him to be more calm, well it's the only different thing we did with both of the dogs he's ever played with, the first time they met he sniffed their bum and his tail went up and started wagging then we took them of the lead and they played.

I was going to try this with my friends dog but he's attacked his dog, but his dog is very calm although the dog is scared of dragon now and always walks away from him, maybe let dragon sniff him and then let him snoff dragon?