[Looking_for_911]

Two years ago I went through this with my girlfriend and her beloved Lab/Cocker mix. That was quite a dog.
We faced the same sort of decisons you're looking at. She tried everything the vets could throw at the dog but it still kept going down hill. I tried to make her understand that the dog's quality of life had deteriorated so much that there was no way it would "happy" again.
She asked me how I knew so much. I told her by looking into the dog's eyes. The look was different from what I'd ever seen. She couldn't see it because she was blinded by the big picture of trying every experimental thing they could to save the dog, but I saw the change that took place weeks into all the treatments, surgeries, etc. The dog was tired and ready to go.
That's one of the hardest things to do, to admit your friend is too tired to go on. And you'll ask yourself How do I know for sure? Maybe the look will be in the eyes.