Trigger Stacking and Coping Thresholds

Does your dog struggle with certain situations, showing fearful, defensive or even aggressive behaviour? Do you ever wonder why they appear to be totally fine with these situations sometimes, and not at other times?

Dogs who are nervous or have behaviour issues can sometimes appear unpredictable, but this is very rarely the case. Trigger stacking and Coping Thresholds are two really useful concepts which will help you understand your dog’s “unpredictable” behaviour, and provide support around things that worry them.

What is a “trigger”?

A “trigger” is anything which causes your dog to feel stressed, worried or uncomfortable. Each dog is an individual, with their own specific fears and stressors. Your dog will have their own set of unique triggers, which will be different to those of another dog.

Triggers can be certain events or experiences (such as going to the vet or hearing a loud bang), particular environments (such as busy areas, or certain walking routes on which they’ve had bad experiences in the past) or more specific things such as certain types of handling, encountering other dogs or unfamiliar people.

Coping Thresholds

Every dog has a coping threshold – an emotional breaking point at which they are no longer able to cope with the levels of stress that they are currently experiencing. Once a dog is pushed over this threshold, they will react in some way. For many dogs, reaching the coping threshold will cause an aggressive response. Others may panic and try to flee, or shut down entirely. Like people, individual dogs will have different coping thresholds, with some reaching breaking point more quickly than others.

Trigger stacking

“Trigger stacking” occurs when a dog is exposed to a number of triggers all at once, or one after the other within a short time period. When your dog encounters one of their triggers, their underlying stress level rises, pushing them closer to their coping threshold. Different triggers will increase the underlying stress level to different extents, depending on how stressful the dog finds that particular trigger (the scarier the trigger, the bigger the rise in stress).

This increased stress level can last anywhere from 20 minutes up to several days, depending on the individual dog and the severity of the trigger. This means that if another trigger is encountered before the underlying stress level has returned to normal, the stress increase from this new trigger adds onto the stress from the previous trigger.

Each additional trigger “stacks” on top of the last, pushing the dog closer and closer to his coping threshold. If your dog is exposed to enough of his triggers at once (or over a period of up to a couple of days), he will be pushed over threshold and show a reaction.

The above diagram illustrates how trigger stacking can work, using the example of a newly adopted dog. We can see that this dog has some joint pain issues; physical discomfort is a common trigger. In addition to this, he has just moved into a new home environment – this is quite a severe trigger for him, adding a significant amount of underlying stress. Further stress is added by being around unfamiliar people. This trigger is fairly minor, suggesting that he is probably quite sociable with people normally, but even very friendly dogs will find moving in with a new family stressful to some extent!

Next, we add additional stress when the dog is taken for his first walk in an unfamiliar environment. At this point, he is already very close to his coping threshold! He then encounters an unfamiliar dog on his walk, which pushes him over threshold and causes him to bark and lunge. This final trigger is not all that severe on its own, but at this point, adding only a minor amount of stress is enough to cause a reaction. This dog is probably sociable with other dogs under normal conditions, so his adopter is probably shocked at his seemingly unpredictable response!

Notice how if even just one of those triggers was removed, the dog would have stayed under threshold and not reacted aggressively towards the other dog. For example, the adopters could have waited for a few days after adoption before taking him out for a walk. This would have allowed some of the underlying stress caused by the new home environment and unfamiliar people to reduce, before adding the final two triggers.

Trigger stacking explains why dogs can sometimes appear to be unpredictable. Often when a dog reacts with extreme fear or aggression, we are surprised because the dog is “usually fine” in that scenario. In fact, the dog has always found the scenario stressful to some extent – but there just haven’t been enough triggers present previously to push the dog beyond coping threshold. Combined with enough additional triggers, the scenario has become enough to provoke an aggressive response.

Some triggers may even be enough to push your dog over threshold when encountered on their own, if the dog finds that trigger stressful enough. For example, a dog who has dog-reactivity issues might be pushed over threshold simply by encountering another dog, even in the absence of any other triggers.

Triggers are typically things which cause your dog to feel negative emotions. However, things which make your dog very excited can also add to the underlying stress level – the more hyped up your dog is, the closer to threshold they are likely to be. Tiredness can also be a trigger, so if your dog has had a fun but tiring day, they may be closer to threshold.

Preventing trigger stacking

Once you understand the concept of trigger stacking, you can start taking steps to prevent your dog from reaching his coping threshold. This is especially important whilst your new dog is settling in. It is also important if your dog is reactive, has ever bitten, or has shown aggressive/defensive behaviour in the past; by being aware of his triggers and working to keep him below threshold, you can help to stop these behaviours from happening again.

• Make a list of all your dog’s known triggers. Try to avoid these triggers whenever possible. You can also contact us for advice on how to help your dog feel more comfortable with them, if you adopted your dog from Forever Hounds Trust.

• Be aware that when your dog encounters one of his triggers, or has a stressful experience, he may be closer to threshold for the next 24-48 hours. Try to avoid any of his other known triggers, any stressful or extra exciting situations, or any situations in which encountering triggers is more likely for at least the next day. This will give him a chance to reset and prevent him from being pushed over threshold.

• Remember that by the time your dog is pushed over threshold and reacts, he has already been feeling uncomfortable for some time. The aim is to step in and remove triggers before he reaches that point.

• If your dog is reactive, has a lot of triggers or frequently goes over threshold, try to avoid activities which will increase his excitement levels (such as high energy toy/chase games, exciting walks etc). Stick to calm, relaxing activities such as quiet walks, food filled toys, long lasting chews, foraging games etc.

• Remember that if your dog is injured or feeling unwell, he is likely to be closer to threshold than he would normally be, and therefore less likely to cope with additional triggers. Sudden changes in behaviour are often due to an undiagnosed medical issue.

• If your dog does go over threshold unexpectedly, try to look back at the last 24 hours and figure out which triggers may have combined to push him to that point. This will help you to avoid a similar scenario in future.

If you are having any issues with your dog’s behaviour, please get in touch with us for advice and support.

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Reviewed April 2025

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