If you have a dog that growls or acts aggressively towards strangers, it’s not too late to do something about it. But first, you should understand why your dog’s acting this way.

Your dog’s ancestors were aggressive by nature. Living in the wild meant having to hunt for food, and defend themselves from other animals. It was instinct to protect their resources like food, mate and territory.

While selective breeding over the last few centuries has definitely minimized this natural trait, all dogs are still capable of causing serious injury.

The good thing is, there is a lot we can do as dog owners to prevent this aggression from surfacing. And if it does surface – for whatever reason – there are things you can do to deal with it.

Aggression in dogs comes in different forms. Aggression towards strangers is one of the most common types. The reason for this type of aggression is nerves. A dog that becomes nervous around unfamiliar people is seeing them as a possible threat. His instinct is to protect himself (and you) from this threat.

A dog that’s nervous around strangers will act one of two ways. He won’t be able to sit still – he’ll be fidgety, he’ll jump at the slightest sound, and he may pace back and forth while barking or whining. Or… He’ll be completely still – staring hard at the stranger, whether it’s the mailman, an unfamiliar guest, or a person approaching you on the street.

A dog who acts this way around strangers hasn’t been exposed to new people very often. The only way he’ll learn that strangers aren’t a bad thing is through experience. He relies completely on you to broaden his horizons – to take him to different places where he can meet new people. Until that happens, he’ll be unsure of new people… which is what leads to stranger aggression.

This process is called socialization, and it’s one of the most important parts of owning a dog. It should be started when he’s a puppy – as soon as he’s had his vaccinations – and continue throughout his life. This lets your dog become accustomed to the world around him. Giving him more and more new experiences is vital to raising a dog that’s relaxed and stable in new situations. This means exposing him to a wide variety of new experiences, new people, and new animals.

You can’t just bring an adult dog into a crowd of new people and expect him to stay calm and relaxed. Saying “It’s okay, Trixie. Settle down” doesn’t work. Your dog needs to learn that it’s okay on his own. Socializing your dog helps him learn this. You want to expose him to all sorts of people — small children, teens and old people, kids on skateboards, delivery people in uniforms — anything that’s different from what he’s use to seeing at home.

When you start socializing your dog as a puppy, he learns that new experiences are a good thing, instead of something to fear. He’ll be much more relaxed and comfortable when he’s around strangers.

A fun way to start socializing your new puppy is to sign him up for puppy preschool. These puppy classes are usually held at vet centers or some other indoor, controlled environment. It’s a series of classes created specifically for puppies and their owners.

Puppy classes are usually taught by a qualified dog trainer. Many times the instructor will bring one or two assistants, which lets you have more one-on-one time with a trainer during class. You’ll learn about your puppy’s developmental stages, how to crate train and potty train your puppy, and even a few basic obedience commands.

This obedience work is a great way to start your puppy on the road to being a trustworthy and well-behaved dog, but it’s really just a “bonus” to the real benefit of puppy classes… which are the play sessions. Several times at each class, the puppies get a chance to run around off-leash and play together. This gives them a chance to learn social skills in a safe, controlled environment. Playing in a group of unfamiliar dogs and people helps them learn how to interact with strange dogs and that they don’t have to be afraid of people they don’t know.

As good as puppy school is, socialization doesn’t stop there. It should be an ongoing experience throughout the life of your growing puppy and adult dog. Take him to as many new places and environments as you can. Just be careful not to overwhelm him. Start off slow, and build his confidence gradually. If you’re consistent with socializing your dog, he will grow into a friendly and confident dog – with no reason to fear strangers.