I only read this post right now and I'm so happy to know that Barney doesn't have bone cancer. I hope you can find a loving, forever home for him to spend his senior years.
Your project of doing water therapy sounds terrific. One thing you could try also is giving him organic Flaxseed oil. It lubricates the joints, I give it to my arthritic old girl. It has Omega 3 which is good for joints and other things.