There is some good advice about. Fear aggression is hard work for both you and the dog. Gentle techniques are awesome, but there also has to be some consequences....

First, work with both the vet and behaviouralists on this. Fear aggression can be reduced with anti anxiety drugs. Its very hard work. We had a dog with severe separation anxiety and OCD. We worked with him for 5 years, we trained him daily, 5-6 times a day, we walked him off lead for 30 minutes every afternoon and 30 minutes on lead every morning. We did training classes once a week. He was medicated and we worked very hard for him and us. Unfortunately after 5 years he developed severe arthritis and became fear aggressive. I was walking him and a child ran out to the fence to see the dog, he attacked the fence. It was one of the most devestating things to go through. The child was fine, it was just knowing... knowing that I had done everything possible and did not succeed. I was in love with this dog, and we spend thousands on him... but we had to put him to sleep. He was unpredictable and I couldn't have it on my head if he had actually gotten to the child. I realised that I couldn't be responsible for it.

So saying that, I don't think you have to make the choice now, but give yourselves some guidelines and draw the line at the decision. Do it now because having to make that decision on the fly was the hardest thing I'd ever done.