Little Benny came from carrick pound a few years ago and went straight into foster with a very lovely family. 
it became apparent from the outset that Benny was terrified of children, His foster mummy did her best to keep him seperate from her children, and over time she noticed that Benny didnt like strangers, and even some people who he knew he would be ok with for a while and then start attacking them for seemingly no reason.
It was a lot of stress and work for this great lady so Benny came back to us to see if we could help him.
Benny is unpredictable with other dogs and people, (except me and rob) can be your best friend one minute and attack the next... needless to say, because of this he was removed from rehoming some time ago! 
However i was still at a total loss as to why he is like this. He would be fine with our dogs one day, and try to kill them all the next....
Then by chance a month or two ago, i was giving him his biscuit at bedtime (a routine they have all enjoyed for years) and i saw it.... 
he let me know what was wrong.
I gave him his treat, he took it and then for a few seconds.. Benny was gone... his eyes glazed, he stared at the biscuits and then me like i wasnt there... it only lasted for a few seconds, before he was back.. but feeling scared. he snuggled into me, and it was a few minutes before he would attempt to eat his biscuit.
He has a form of epilepsy.. that is casuing little "abscences" and these are probably enough that during those moments of "unpredictability" he is suffering from, or coming out of one, and feels anxious and scared. 
with Benny, this anxiety comes out in a defensive form when he is around other animals/people he doesnt truly trust.
hopefully medication will help him, but even if it doesnt, i know he trusts me fully, and he has a happy life with us. 
unfortunately we cannot put him up for rehoming (even if the medication works) as the risk of him biting woudl still be there, and its part of our job not to put the public at risk.
We will do our best to keep benny as happy and content as we can, and hope to get to the stage where his behavio
ur around the other dogs is good enough that he can come live in the house. 
For now he has the kennel and run beside Grace, so is great company for her and she for him, and he comes out for walks amongst the others in a muzzle.