The best way to keep dogs away from the Christmas tree is to make sure it's secure and well-anchored to the ground. You can also place a gate around it or use physical barriers like tables or chairs to prevent the dog from getting close. If the dog is particularly persistent, you may need to train it to stay away from the tree using positive reinforcement techniques such as treats and verbal praise. Additionally, providing the dog with alternative activities and distractions such as toys and bones can help keep it occupied.