Thanks so much guys... I've called the vet and made the appointment.
Ultimately, I knew it was my only choice but I needed some serious reassurance from other animal lovers and I got it from you guys. I really appreciate that.
I've rescued multiple dogs, some moving on to other homes and some staying with me for life. I've never ran across one that I just couldn't "fix" so to speak. I'm the girl that goes to the shelter, asks who's on death row then picks the one out of that group that looks plain hopeless. Train him or her then rehome them successfully many times. This one, no matter how much time I spend, it's not possible.
Today, my border collie mix gave me a clear message and I took it. I was walking towards his fence to be sure his waterer was full, she ran towards me and blocked me with her body, nudging me *away* from his fence... I think Abigail knows he's not okay. She's never pulled anything like that in the past... In fact, she loves everyone and everything.
Again, thank you so much... I'm going out to buy him a cheeseburger and scramble him a couple eggs. Also fill up his kiddie pool for him today. It's hard... but it would be even harder if he killed one of my other dogs or injured a human. And it would be highly irresponsible if I ditched that on someone else.