Man’s best friend is usually a pretty friendly animal. He likes to pant and lick—sometimes to the chagrin of his master, and definitely his master’s cat-people friends—and wag his tail. He likes to chase cars (but like the Joker says, wouldn’t know what to do with one if he caught it), balls, sticks and bunnies. He likes his ears ruffled, his tummy scratched, and to sleep at the foot of your bed. All in all, dogs are pretty loyal companions that love to the end, as their stereotype has always suggested.

But some dogs just aren’t. Whether they’ve been rescued from a bad home, used in the “ring” as fighting objects, were taunted or teased as a puppy, or they were exposed to Cujo on network television (with even scarier commercials about getting worm medicines mailed to your home), some dogs really are man’s worst enemy.

You probably know one of these dogs yourself. Maybe you have a friend who warns you, “Don’t pet Missy—she bites sometimes,” or you had a neighbor who was badly bitten by an angry dog. Does this make the dogs bad dogs? Not necessarily; but it does make them unsafe pets, which leads to the question—what do you do with a dog who is violent?

If a dog is aggressive, the first thing that should be done is to visit a vet. He or she can determine whether or not the aggression is normal or not—as well as if it can be fixed or not. He or she might run tests to see if the cause of the aggression is a medical one. Conditions such as low blood sugar, a brain tumor, liver disease, lead poisoning or encephalitis can all cause this behavior.

Some say that these dogs can be trained to adopt more gentle behaviors. This could be true. After all, there have been violent humans who, after being sent to therapy or an institution of some sort, were able to be “cured” of their violence. A vet can recommend a behaviorist or other course of treatment for the dog to help modify behavior.

But what if the dog is really aggressive and biting people—a real threat? Up to a million dog bit injuries are reported every year, and while about half of them were provoked, the other half can be attributed to canine aggression. If a dog bites, it’s normally out of pain, fear, defense or a desire to protect its territory. A behaviorist may be able to help in some of these instances as well.

Have you ever had a violent dog? What did you do with him or her?