If your dog is regularly munching on everything, whether it is edible or not, it might be suffering from Pica.  In the event of Pica, eating objects such as rocks, chalk, fabric, diarrhea, and plastic can cause gastric discomfort, vomiting, diarrhea, and, in the worst-case scenario, intestinal blockages.  Limiting your dog's access to non-nutritive objects such as plastic, rocks, and string is the most effective strategy to keep them from consuming them.