There is a product that you can buy that you add to the dogs food. When it passes through their system, it will leave the poop with an unpleasant taste to the dog. You put it in their food for a couple of months ans the dog learns that poop does not taste good and afterward leaves it alone. I can't think of the name of it, but a Veterinarian could tell you what it is. As far as grass eating most dogs eat a little every now and then. It usually makes them vomit.