I honestly believe that Pro47 has a point. Its very hard to hear i'm sure, but its more or less the best for him. Aggresive dogs always have a reason for being aggresive.
Ie; dominance over everything, personality default, mistreatment, in pain.
Our first Sheltie came from a reputable breeder(whom Crosby is named after, he was a deal friend of the family as well). but, Meaghan was diagnosed with doggy "AIDs" and there was obviously no cure for her. She didn't even last a year, but as she got older her condition worsened so did her temperment. She attacked our other dogs frequently. SHe was tested for everything until we found out about her condition. She was on a bunch of medication that totaled over $1000 within a short few months. But she was worth everything that we paid for her... but finally, after her attacking(or trying to) a friend of ours... it was decided that she was PTS.
Sometimes, even though you try your best, things are just not meant to be.
I'm sure while Mack was with you, you provided him with an amazing home and you had done everything for him that you could have.
Pro is also right about Hannah, spend all the quality time you can with her! Make sure you include her on everything when you get your poodle pup too, because after she is getting 100% attention, she'll wonder what happened or what she did when the poodle pup comes along and they get the attention.