Here is the post I have used in the past to explain how urine kills grass. It is incredibly informative and explains the science behind the grass dying.
" Dog urine contains ammonia and salts and these are hard on grass. The ammonia causes the soil to be more acidic, which is also stressful for grass. One easy solution is to add dolomite lime to the urine spot. Dolomite lime helps to neutralize the acid in dog urine and restore the soil to a pH balance more favorable to the growth of new grass."
We have added dolomite lime to our dying spots and it has helped dramatically. I purchased a bag at Lowes.
Hope this helps! Lauren - The Little Lake Cottage
There's also a stone you can purchase to put in your dog's water bowl. It's supposed to help with the acid in the urine as well. Good luck!
Hello. I have trained my dog ( current and past) to pee in the mulch) over the past 19 years -so I may not be aware if all possible solutions but this product is fairly new, and I have not oersonally tried it. It may be worth investigating researching reviews and Q+As.