Trigger stacking is the process of meeting a lot of triggers in a short amount of time, to the point that the dog can no longer cope at all.
Without the opportunity to calm between scary experiences a dog’s stress levels will continue to rise. The point where a dog can no longer cope is called his coping threshold. You may hear or have read the term threshold before, it basically means a dog’s breaking point. Sometimes a dog will react quickly and to one scary experience, whilst at other times he will stay below his threshold and achieve enough space and time to recover, so he never reacts. But once a dog has reached his threshold he is likely to react to all triggers until he is given the opportunity to calm down, over as long as 72 hours.
When a dog has a poor ability to cope with triggers in the environment and we can manage those triggers. We can keep the dog below threshold by managing our dog’s safe space and increasing distance between our dog and his triggers. If a trigger enters a dog’s safe space without warning, and sends the dog over their coping threshold, the dog is then likely to become hyper-alert and likely to react more quickly for the next few hours.
A real-life example is this. A dog that is scared of children may cope with a child ten meters away at the park, playing quietly (trigger 1). If the distance stays the same but the child begins to scream (trigger 2), the dog may not cope as screaming has added a second trigger and the entire thing has naturally become a scarier scenario, so the dog may bark. However, if the dog can cope with the screaming and stays under their threshold but then another screaming child runs in (trigger 3) that might be just too much for the dog and he will go over threshold and react.
If the dog is really resilient despite his fear of children, he may cope with these three triggers at a safe distance; but if a third child appeared a little closer, the dog may go over his threshold and react.
These triggers don’t need to be related at all. A dog who is scared of unknown people may walk by three strangers and react on the fourth. Not because there is something particularly scary about stranger number four but because four strangers are all the triggers he can take in the short amount of time that he met them. When we have this knowledge; we start to get a much better understanding of what our dogs are experiencing when they are out in the world. The point that they react to something is not random. The reason is always there - if we look carefully and learn to read our dogs, we will be able to see it.
Trigger stacking is often the reason that a dog may bite. He can cope with things on some days, when he is generally relaxed, but on other days, maybe after a few scary experiences, he may not be able to cope with exactly the same thing. A dog on a TV chat show for example, may never have bitten anyone in his life but add the light, acoustics, heat, chaos and smells to a presenter that forces a hand or face into the dog’s safe space and we have a trigger stacked dog that goes over threshold, simply because he can’t cope anymore. This may lead to the dog biting the TV presenter.
We could have a calm dog leaving the house, but then we go to the vets. We leave the vets and pass a noisy digger on the way to the park and a few minutes later a storm blows in. Until now our dog has coped remarkably well, then a stranger tries to talk to him. We lose our opportunity to increase distance between our dog and this final trigger; the dog goes over threshold and reacts. We then spend the rest of the walk dealing with a dog that is over threshold and simply can’t cope with any trigger that he sees.