Hi there Hugh,
I'm sorry to hear that your dog has kidney disease. One of the best supplements for dog kidney failure is called Azodyl which provides natural dialysis and slows down toxin build-up to prevent further kidney damage. I manage the blog here at Probioticsmart.com and would also like to point you in the direction of a blog post with more information on this topic: Dog Kidney Failure. Good luck and please let us know if you have further questions.