[anonymous]

Do not give supplements unless recommended by a veterinarian that has examined the dog.

Do not give supplements that are not approved for veterinary use unless prescribed (off label) by a veterinarian that has examined the dog. Many over the counter meds and supplements intended for humans can include ingredients that are toxic to animals.

For stubborn cases like your dogs, there are prescription medications the vet may recommend. I might consider consulting a Veterinary Internal Medicine Specialist.

https://vcahospitals.com/know-your-pet/calcium-oxalate-bladder-stones-in-dogs (excerpt below)
How can I prevent my dog from developing calcium oxalate bladder stones in the future?
Dogs that have developed calcium oxalate bladder stones in the past will often be fed a therapeutic diet for life. Diets that promote less-acidic and more dilute urine are recommended. Most dogs should be fed a canned or wet diet to encourage water consumption. Dilute urine with a low urine specific gravity (Urine Specific Gravity or USpG less than 1.020) is an important part of the prevention of calcium oxalate bladder stones. In certain cases, medications to lower the urinary pH such as potassium citrate may be required. If the dog is fed a home prepared diet, Vitamin B6 is often added as a supplement. Dogs that repeatedly develop calcium oxalate bladder stones without high blood calcium levels may benefit from hydrochlorothiazide treatment.
Dogs diagnosed with calcium oxalate stones should avoid calcium supplements unless specifically advised by your veterinarian. They should not be fed high oxalate foods such as chocolate, nuts, rhubarb, beets, green beans, and spinach.
In addition, careful routine monitoring of the urine to detect any signs of bacterial infection is also recommended. Bladder x-rays and urinalysis will typically be performed one month after treatment and then every three to six months for the remainder of the dog’s life. Dogs displaying any clinical signs such as frequent urination, urinating in unusual places, painful urination or the presence of blood in the urine should be evaluated immediately. Unfortunately, calcium oxalate stones have a somewhat high rate of recurrence, despite careful attention to diet and lifestyle.
Contributors: Ernest Ward, DVM