Onions are toxic to dogs, and can make them sick, though it requires a quantity to be fatal, depending on the dog. Keep onions away from him. Little slivers are okay now and then, but it's better to be safe than sorry.

Slow Malone down, if you want, by putting a large rock or something in his dish, but that's not the real problem. Owners of Great Danes and other large deep-chested dogs are always told NOT to let the dog exercize hard or play right before or right after eating - not for an hour or so after eating. A normal-paced walk is okay, that helps digest the food, but no running right after eating.