While I am not a Vet, I do know a lot about dogs as I selected and trained working K9s for the USMC, was a K9 LEO for a bit, and helped run a kennel of some of the highest quality protection dogs in the country. The wife and I still have a kennel on our farm that offers day care, boarding, and fosters older dogs in their decline and young pups until they find their forever homes. We currently own 3 dogs, have 7 foster pups, and 10 kenneled boards so 20 dogs keeping us busy. K9 nutrition is a huge part of our way of life, as our dogs are our lives. We never leave them. We even bring them on vacation and most of the trip is planned around things we can do with them by our side. We have encountered almost every health challenge from injuries to allergies to surgical recoveries to just plain old geriatric old age and in most all cases we have been able to offer some type of intervention (with the help of both an old school and new progressive integrative and holistic vet) that helped.
While, yes, Taurine and Astragalus will indeed help your dogs kidney disease and Omega3 is also very important, it is also equally important to look at your dogs basic diet. Just like us athletes, if the baseline diet is lacking or inappropriate, no supplement or even Rx is going to make much of a dent in declining health. I have watched a dog recover from a lifelong neurodegenerative disorder that nearly had it crippled to thriving and chasing frisbees over the course of six weeks from nothing more than a dietary change.
You didn't mention anything about your dogs diet or general health. How old is he/she? Any health conditions other than the kidney disease? Overweight? How many times a day does he / she eat? What do you feed him/her? What other supplements do you provide? Breed (yes, certain breeds are susceptible to specific conditions and diets that treat illness can be breed specific).
Lastly, you asked what else will help. Probiotics can help K9 kidney disease quite a bit. Check out a product called Azodyl.
These animals are the greatest gift we humans have. Unconditional love like no other. I consider myself very lucky to have had a life surrounded by and steeped in K9's. They just become part of your soul. I will do anything I can to help.....
Feel free to DM me.