My dog Sadie ate a bunch of shale from our lane. Due to the jaggedness of the shale, the vet did surgery to remove it from her stomach. She is recovering well, but she still wants to try and eat shale. She loves to be outside with us but when we are busy, we can't keep a constant eye on her. I have to make a decision on what to do. A shock collar is out of the question. I've been leaning towards a special muzzle when she is outside. Your thoughts? This pic is the shale that was removed from her stomach.