Make untrapping deterministic based on a hash of the object ID (for containers) or xyz coordinates (for doors), so that you only ever need to search for traps once and there is no benefit to repeating the command.

The computation should amount to finding a number representing how hard the trap, if present, is to find. Any bonuses from your role and experience level can raise the threshold of traps you are able to find.

An alternative way to do it is to define a third outcome: you are skilled enough to find the trap given enough time, but it will take longer than is usual for #untrap to find it. This would be better if untrapping were first turned into an occupation.