Stop biting your lips and causing damage to your own body. Instead, cause damage to an inanimate object, such as a pencil or piece of food. There is no reason why you should not snack on food to prevent yourself from tearing up your lip.
When you see the bite marks on a pencil, see how much you have been gnawing on your lips. Then, you are more likely to stop this destructive habit.
Do not make it a habit to bite down on a pencil, though. You should not be biting down on anything except food. It takes a good amount of self will to overcome this, but with a lot of time and patience, you will stop these habits eventually.