A dog that lunges at other dogs on the lead is frequently described as untrainable in that situation. The obstacle is usually distance rather than the dog.
What a threshold is
Every dog has a distance from a trigger at which it notices but can still function — take food, respond to a cue, look away and look back.
Closer than that point, the response shifts. Food is refused, cues produce nothing, and the dog fixates. The change is often abrupt rather than gradual.
That shift marks the boundary between a dog that can learn and one that cannot. Nothing useful is taught on the wrong side of it.
Why learning stops when it does
Strong arousal narrows attention and prioritises immediate response over deliberation. Systems that support flexible learning are suppressed while it lasts.
Refusing food is the most reliable practical indicator, because appetite is one of the first things to switch off as arousal rises.
Repeated exposure above threshold does not habituate the dog. It rehearses the reaction, and rehearsal makes it more fluent rather than less.
Finding the line in practice
The threshold is measured, not assumed. It is found by working at a distance where the dog is clearly comfortable and closing in gradually while watching for the first change.
The early signals precede the obvious ones: a stilling of the body, a closed mouth, a fixed stare, a pause in sniffing. These appear before any lunging.
It is not a fixed number. It varies with the trigger's size and movement, the surface, the dog's sleep and recent experience, and how many triggers appeared earlier in the same walk.
How the distance is closed
Below threshold, the trigger is repeatedly paired with something the dog values, so that its appearance begins to predict a good outcome rather than a confrontation.
The measure of progress is what the dog does on noticing a trigger. A dog that looks at another dog and then turns back to its owner has changed its expectation.
Distance is reduced only once that turn is happening consistently, and it is reduced in small increments. A single incident above threshold undoes a great deal.
Why environment management is part of the training
Progress made in structured sessions is lost if the dog is repeatedly overwhelmed during ordinary walks, because those exposures are practice at reacting.
Choosing quiet routes and times, using distance-creating turns, and accepting that some walks should be skipped entirely are all part of the protocol rather than avoidance of it.
Reactivity with a bite history, or directed at people, calls for a qualified behaviour professional working alongside a veterinarian rather than a self-directed plan.