Hi Ash,
Here's the bottom line: you know Chewy and we don't. It is my first instinct to beg you not to put him down. But after having worked with some aggressive dogs in shelters over the years, I am starting to understand that some dogs are just ... aggressive. I know you've been struggling with this for a long time and have even had professional help. I applaud you for trying to fix the problem for so long. Maybe a behviorist and a new environment could fix him, but maybe not.
Many people decide to just keep aggressive dogs but they'll keep them locked up all the time so they don't have to deal with it. That is no life for a dog and sometimes they are better off laid to rest (I can't even believe I'm saying all this - its so hard for me).
At the end of the day, the decision is yours and your family's. I know Chewy is so young, but some of the things you describe have been really scary and don't seem like normal puppy behavior. What if he gets older and gets 10 times worse?
I would tell you to seek second and third opinions and so forth, but I think you have done that.
Its just so hard for us to judge because we can't see it. I'm sure its much worse for you to witness and it might not sound so bad when you type it on the computer because people are removed from the situation.
Oh yeah, never hit or use physical violence on an aggressive dog. 99.99% of the time it makes it muuuuuuuch worse.
So anyway, what I'm trying to tell you - don't feel bad about your decision. You are the one in the situation who knows all the details and all the horrific experiences. Not letting go of a child's arm is VERY VERY VERY bad. Please feel confident and seek comfort knowing that you made the best decision you could. I know you would not put him down if not absolutely necessary. I'm crying so much right now. I'm a big softie who believes every dog should live ... but I am starting to understand and become less naive about just some dogs need to be put down :( poor Chewy.
My prayers are with you. I know it will be very hard. Please spoil him for his last days :(
** sorry I sound like a babbling idiot - hope you get the gist of the message though :(