Not to be alarmist...I know it can be hard to totally stop them from doing it, but be careful. Our sheltie got a tapeworm from eating rabbit poop (the vet called it "doggie caviar") from the backyard.
He had been lethargic, losing weight, and having bloody dumps for a few days. We took him in to get checked out and the vet asked if we had a rabbit. We don't, but we get a lot of them in our yard. He said the dog had picked up a worm commonly carried by rabbits. It cost nearly $1500 to get him dewormed and back to normal. The things we do for our pets...