1. Your dog is spayed or neutered. Your dog's risk doubles with the removal of the sex hormones.
2. Your dog is getting older. Yes, you read that right. As your dog gets older, the risk goes up. But you don't have a lot of options here.
3. Your dog was a chubby puppy. Although pudgy pups are cute, they become overweight adults. Not so cute.
4. Your dog has access to food 24/7. Most dogs don't stop eating when they are full. They stop when the food is gone.
5. Your dog eats lots of processed treats. Just as in people, its easy to take in lots of empty calories quickly when eating tasty processed snacks like dog biscuits, imitation pepperoni or bacon treats, or worse yet, chips and crackers! Okay, I don't know many people who eat dog biscuits, but you get what I'm trying to say here.
6. Your dog is a couch potato. Lack of exercise means the metabolism is going to be slow and not many calories will be burned. Its easy to eat more than you burn if you don't move much. Plus lots of other good stuff that promotes fat loss happens when your dog exercises.
7. Your dog eats a diet high in carbohydrates. Excess carbohydrates gets stored as fat. Combine a diet high in carbohydrates with little to no exercise and you've got a recipe for obesity.
If you want to keep your dog from getting fat, then lower your dog's risk factors. You have control over several of them. Do right by your dog. As they say, be the person your dog thinks you are.