I shall rise above the insults to come back and say that it is the worry that the dog will hurt or maim or even kill a child.
I have had some behavioural training, I went to the States a few years ago and did a study for my final year dissertation on dog bites and baiscally who gets bitten.
It worries the hell out of me to let a dog that has bitten a child out of the surgery, even if to a very experienced behaviourist.
You see, the sucess is to have a dog that never bites again.. but if the behaviour therapy fails, this could end up with another bitten child, or worse.
Sorry, but that is how I sleep at night, I am not a hard or dispassionate person at all, and have wept at these sorts of decsions when I have had to do it. But I have slept at night... and I don't think I could if I felt that I had been instrumental in potentially having a child fatality on my hands.
The old couple who live in the cottage away from any children is a lovely haven, and it would be fantastic if that place existed for every dog who exhibits challenging behaviour.
But I always worry that children get into people's gardens etc- or out on walks they meet some kids etc.
I don't make these sorts of decsions lightly and happily have only had to do it a few times in my career.
Maybe I have spoken out of hand, i usually spend a good deal longer with the owners and discuss the whole situation at length and last night I did only read the first few posts and I would certainly listen to the situation and hear how the dog was otherwise.
But if an owner is so unsure about herdog then it would worry the hell out of me to rehome the dog i am afraid.