A dog trained thoroughly as a puppy often responds poorly at four years old despite nothing having gone wrong. Trained behaviour is maintained rather than owned.
Behaviours compete rather than persist
A cue does not sit in isolation. At any moment several behaviours are available, and the one that occurs is whichever has the strongest recent history of paying off.
A recall that is never rewarded still exists, but it is competing against sniffing, chasing and greeting, all of which deliver immediate results.
Decay is therefore a shift in relative strength rather than forgetting. The dog has not lost the behaviour; the behaviour has lost the competition.
The order in which it falls apart
Degradation follows a consistent sequence. Reliability under distraction goes first, then reliability at distance, then latency, and finally the behaviour in easy conditions.
Owners typically notice at the third stage, when the dog responds but slowly. By then the first two have been eroding for a long time.
Because the kitchen version survives longest, dogs often appear fine at home while being unreliable everywhere that matters.
What accelerates it
Repeating a cue into no response is the fastest route to decay, because it teaches that the word does not require action.
Using a cue only for outcomes the dog dislikes does similar damage. A recall used exclusively to end walks and clip a lead acquires a predictable and unwelcome meaning.
Long gaps in use matter less than these two. A behaviour maintained occasionally in varied contexts survives far better than one used daily in a poisoned way.
Maintenance costs less than repair
Keeping a behaviour requires much less work than establishing it — occasional practice in varied settings with unpredictable reward is generally enough.
Building it into ordinary life is more sustainable than scheduling sessions. A recall practised twice on each walk, at moments the dog is likely to succeed, needs no separate time.
The rebuild after full decay takes considerably longer, particularly if the cue has been said into silence for months.
Ageing changes what maintenance means
A behaviour that deteriorates in an older dog is not always a training issue. Hearing loss is a frequent and easily missed cause of an apparently ignored cue.
Joint discomfort can make a sit or a down genuinely unpleasant, and a dog avoiding a position is often reporting something rather than declining.
A sudden change in a long-reliable behaviour in a mature dog is worth checking with a veterinarian before more training is added on top of it.