Have made an appointment for Thursday for Walter's final trip to the vet. I'm pretty sure it's the right thing to do, he has less and less control over his body, but I'm sad to have to make the call.
When he was a pup we used to take him to the levee at the Fly to swim in the Mississippi (it was technically not supposed to be an off-leash area but a lot of dogs were running around there). He loved fetching sticks out of the water. Once he got hold of a bush or something that was either rooted in the bottom or snagged on something - it did not budge. He just kept paddling and tugging on it, doggedly, as they say, and I was legit worried that he would tire himself out and not be able to get back to shore. He did finally "drop" it. I think that's what he's doing much of the time now, just not wanting to give up however hard it gets.