What can I do about stinky yellow grass from my 2 dogs?

You need to put out lime frequently...urine is acid and lime cleans the yard. You do not need to test your soil to find out if you need it, the yellow , stinky grass is screaming for lime. Always make sure you dump a handful on poop!!! It will help it decay faster.

Lime. Lime is an alkaline substance that raises the pH of the soil. Many soils have naturally occurring lime -- especially if they are highly alkaline -- but those that don't benefit from adding lime. Most lime is calcium carbonate (CaCO3), and is often called "agricultural lime" or "ground limestone."

First, supervise their "pee time" and get them into the habit of using the same spot to do their business. Next, water the old spots with lots of water to dilute the ammonia in the pee and the grass should come back.

I would water frequently to wash the urine into the ground off the grass. Make sure the dogs drink frequently in hot weather to dilute the urine. Before you use any additive to your soil, get a soil test to make sure it remains in pH balance.

Make a potty area for the dogs, with gravel maybe behind some bushes and train them to use it.

There are supplements you can give dogs to eliminate the grass getting burned by the urine. We live in a large neighborhood where just about everyone has dogs, many of them walked a couple of times a day. So far, we have not had a problem with yellow spots, even at the tree the males all like to urinate at. I guess our soil is just right in our area.