The smell can be overpowering in a small, confined area such as a den. It would be better to live trap the animal and release it after the den has been filled in. However, a large hole typically indicates a woodchuck, fox, or coyote. Woodchucks should have already started hibernating, so a new excavation seems unlikely unless the animal is getting a late start. If the animal is a fox or coyote you should hire a nuisance wildlife control operator to trap the animal for you. Can you make out any tracks around the site?