One product in particular that matches your description is called Dog Rocks. The product claims the following:
Dog RocksŪ filter out impurities from water such as Tin, ammonia and nitrates. These impurities are usually passed out through urine, and when your grass comes in contact with these elements it is burned, resulting in a dead, yellow patch on your lawn.
That's a cute claim, but the fact is, there are chemical components to a dog's urine that result from the metabolism of protein and nothing more (filtering them out is an absurd claim). No water additive is going to eliminate that entirely, and if it does some how "adjust" the chemical composition of the urine, what in the world might that be doing to the kidneys/etc. in the process? The only way to "adjust" it would be to put something into the dog's body to make that happen, and that's a huge risk in my opinion. Be wary of anything labeled "all natural" because there are lots of "all natural" things in this world that can kill us or our dogs very easily.
Just too risky. Some people claim it works, but I think their website sounds like a load of hogwash and I wouldn't want to risk tinkering with mother nature like that.
Better to treat the lawn. One of the best things that can be done is to keep a full watering can on hand, or a hose. Just water down the area the dog urinates on to dilute the urine. This alone can help tremendously. Otherwise, there are lots of lawn products out there to treat the problem.