Dealing with dogs and aggression is challenging for anyone. No matter how long you have worked with dogs or how many letters you have after your name, it's never easy to resolve aggression cases. It's physically demanding and can be incredibly emotionally draining.
According to a quick google search, aggression can be defined as 'feelings of anger or antipathy resulting in hostile or violent behaviour; readiness to attack or confront.'
This would suggest that aggression is not a personality trait but an involuntary response to a feeling or sensation, similar to hunger that leads to a specific behaviour (eating or lunging/growling/barking etc). I am hungry sometimes but not all the time. This is the same for aggression. In certain situations a dog may display aggressive behaviour but they are not acting aggressively all the time. They cannot be asleep and showing aggression at the same time.
Labelling a dog aggressive doesn't give us adequate information. You wouldn't call a lab a 'hungry dog' because they always scoff their food at breakfast and dinner time. It's a response based on an how they are feeling due to a trigger or event.
This is similar to aggression. There will typically be an antecedent that triggers the aggressive behaviour because the outcome is what the dog has previously achieved and is trying to achieve that outcome again.
Aggression will usually have specific contexts. Resource guarding is a very common problem people face, especially in multi-dog households, which usually ends in scraps and scuffles. Aggression is used in these instances to achieve a goal. Defend and keep a specific resource.
Aggression is also a normal response. We show aggression when we feel we need to. A father retaliating to protect his daughter from a potential predator would be hailed a hero. He could show the most aggressive display possible and most of us would still think that's okay. Even then we wouldn't label him 'aggressive'. We would say he responded aggressively due to the horrible situation he found himself in. It was an acceptable response given the circumstances.
When working with dogs that show aggression we have to look at things from their perspective. If we slap the aggressive label on them and shelter them from everything and anything because we are worried they are going to respond aggressively they'll likely get much worse. We need to understand the antecedents which leads to the aggression. Once we understand them, we can change or remove them to reduce the chances of the dog opting for aggression.
We also need to teach them that they can react differently. A simple but really solid recall can work wonders. Our Poodle struggles meeting new dogs. He gets very stiff and will usually growl if he comes across another dog (especially a larger male). If we call him away he can no longer become aggressive because of the space we have created. So we can work through aggression with basic training but we also must understand what and why our dogs respond like this in the first place and what situations are likely going to cause the aggressive outbursts. We know our Poodle struggles meeting new dogs and doesn't like it so we simply don't take him places like the dog park.
If we want to change how the dog behaves, we have to first change how they feel.
If you have been told your dog is aggressive or think they are, write down all the situations where they show the aggression. I doubt you'll have much of a list.
The most common situations we see are:
1 - Multi-dog households usually involving resources
2 - Unfamiliar male dogs greeting
3 - fearful dogs meeting unfamiliar people and dogs.
4 - Predatory behaviour
5 - Handling aggression
In my opinion, this is not only normal but very predictable.
Aggression is normal in all species. It serves an important function. It can keep us safe and it can gain us access to valuable resources. We all use it to some extent and a lot of the time it's appropriate and arguably beneficial. But when it starts to negatively impact an animal's life, we then need to change something to help them cope better.
Aggressive behaviour is expensive. It takes a lot of energy and has the potential for ending poorly for the aggressor as well. I would consider it a last resort behaviour for a lot of dogs.
So aggression is not a trait. Every dog will show some form of aggression at some stage in their life. It's up to us to notice early why it's being offered and then WE need to change our dog's environment and help them cope better. Through ongoing and consistent training we can see a good level of modified behaviour but we cannot forgot that aggression isn't something that gets 'fixed'. Given the right circumstances and antecedents aggression will likely be shown again and again. It's not up to our dogs to change, it's up to us.
If you do see a sudden change and your dog starts showing aggression or becomes more aggressive the first thing to rule out is any pain or underlying issues your vet should be able to check for and advise on. Just like us, dogs are more likely to become irritable or lash out when there is pain. We can tell people we've got a headache or whatever it is bothering us, dogs can't.
For more info, these videos will be helpful: