If you’ve ever been surprised by your dog’s sudden aggression, the following tips will help you diffuse the situation. Once you’re safe, contact a qualified dog training and behavioral professional to help you determine the cause of your dog’s aggressive reaction. A canine behavior specialist will give you techniques so your dog learns better ways to cope with triggers that currently cause aggressive displays and will provide you with management tools to prevent aggressive behavior in the future.
Be calm. If your dog growls over a bone, snarls at another dog, or lunges at a child—your first instinct is likely to scream, “NO!!!!”. Aggressive behavior is unacceptable and dangerous. However, loud scolding can cause your dog to become more defensive which may result in an attack. If your dog is already on a leash, quietly guide him away from the plumber, child, dog (whatever is causing his aggressive display), so he relaxes. By calmly adding distance to the situation, you’ll give your dog an opportunity to recover from the emotional turmoil causing his aggression.
If your dog is off-leash, safety tactics can be a bit trickier. If you’re approaching your dog, stop moving immediately. By walking close to an already agitated dog, you’re communicating that you’re not backing down, and contrary to popular information—attempting to “dominate” a dog who’s aggressing may make the situation worse because you appear menacing, aggressive.
Aggression + aggression = more aggression
You can reduce tension, and potentially stay safer by removing social pressure: pause, slightly turn your head, lower your gaze, and relax your body while remaining still. During precarious moments, your goal is staying out of danger. Communicating to your dog that you’re not a threat is a much better way to prevent a full-blown attack than adding more aggression to an unstable situation. Never turn your back, run, scream, or make sudden movements—all of which can further incite your dog, and place you in a more vulnerable position to become injured.
Once you’ve gained composure, find something of interest to your dog (or if another person with you, she’s in a better position to distract your dog if he’s growling or snarling at you) and as slowly as possible, move the item far away to entice your dog then confine him immediately. Though tossing a treat (underhand is best) into another room may seem like you’re rewarding your dog’s aggression, you’re preventing an attack. You’ll need to make a plan once everyone is safe to avoid further reinforcing your dog’s unwanted behavior.
Practice prevention. It’s important to make a note of what caused the aggression. Did your dog growl over a new a toy? Did a stranger approach your dog too quickly? Was your dog standing in front of you, attempting to protect you from your partner? A good trainer can help you identify what caused your dog’s aggression but until you can schedule an appointment, you must practice management to prevent putting yourself and your dog in a scary situation again. Leashes and gates are great ways to keep everyone unscathed (child, stranger, or another dog) until the trainer arrives.
If you’re unsure if your dog has the potential to become aggressive, thank you for being proactive—here are some tips to introduce a new person to your dog safely.
Understand body language. In my line of work, I meet a myriad of aggressive dogs, some with very serious bite histories. Nonetheless, I remain safe because I watch dogs closely to assure I know what they’re communicating so I’m actively preventing them from becoming so uncomfortable that they want to bite me. Keep in mind, dogs are MUCH faster than we humans are, so it’s best to keep your dog’s nervousness or agitation way below attack-mode because he doesn’t need coffee to gear up, especially in heated moments.
Indications that a dog is close to becoming defensive are hard stare, mouth tightening, pulsating tail (not wagging), and tense body posturing. If your dog positions himself between you and another person, runs away with a toy and hovers over it, or walks away from a child and hides, stop doing what you’re doing, immediately.
Your dog is communicating that he’s uncomfortable. If you pet him, take away his toy, or allow your child to corner your dog when he’s attempting to avoid a conflict or defensiveness, you’re asking for trouble. While I agree dogs should not be permitted to growl at your kids or snarl when you touch his belongings, tense moments aren’t teachable moments. Reduce tension by softening your body language, and when your dog is in another room, pick up the toy and place it in a closet or keep the person at a safe distance until you hire a trainer.
Tense moments aren’t teachable moments.
Never punish aggressive behavior. If you scream, yell, or stick your face in your dog’s face while he’s growling, snarling or snapping, you could get attacked. If you’re still getting to know your dog (it often takes up to a year to really know a dog), and his bite history is unknown, you very well may end up in the emergency room. Adding force and anger to an agitated, uncomfortable, and volatile situation can cause serious injury to you.
If you punish your dog harshly, some dogs stop communicating discomfort to avoid further punishment. Teaching your dog NOT to growl before he bites will jeopardize the safety of everyone you love.
Prevention and understanding are the best ways to keep an aggressive dog calm. However, in the face of a surprise, avoid staring and remain calm. Once you’re safe, call a trainer to get the help you need.
Some dogs happily accept every toy their human brings home and will eat any treat with wild abandon; other dogs need a little more prodding to determine what makes them happy. 
