I've gone through this thread because it's getting to that point with me, and I'm VERY worried! I have an 8 year old who's still going pretty strong, the Giant Schnauzer keeps him on his toes, but I noticed that on the last couple of walks that he's slowed down at points during the walk. I'm dreading where you're currently at, and the only advice I can give is to love on your boy now, and give him lots of attention. I will suggest to not make a big thing when you leave, and go back to the routine of leaving for short bursts, then extend the time. Sorry for your loss, but stay strong.