I used to buy a food item at Wal-Mart that was sold in large bags. Because of their size, the bags were kept on the bottom shelf.
After seeing dogs walking around, with their thoughtless owners, I stopped buying that product. Dogs will piss on anything and everything they're allowed to reach.
Dog owners will, of course, say they keep close watch on their filthy animals. But most of the time, the owners are reading labels, or otherwise preoccupied, and their dog is allowed to roam the entire aisle freely at the length of it's leash.
Sickened by this filthy possibility I stopped buying ANY grocery items from Wal-Mart. If they're going to sell food, the least they can do is keep dogs away from the area in which it is stored.