On Guard (sage ability)
On Guard is an amateur-status sage ability that ensures a character acting as a sentinel — and taking precautions against unknown enemies — can be surprised only on a 1 in 6. This describes any situation where the character actively states that he or she is on guard. It cannot be applied to situations where the character is striding along, otherwise moving or engaging their attention upon something other than watching for trouble.
A character standing among a party, however, not conversing, searching through his or her equipment, or otherwise engaged in activity, can declare their status as being on guard. This may require explaining to the other members of the party that the character should be left alone until any possible danger is past, or the "on guard" stance is relaxed.
Those with the ability are limited to a time period of 3 hours, +15 minutes per level, before they must relax their stance and lose the benefit. This does not mean they cannot continue to guard, only that they will be surprised normally. Guards cannot space the benefit throughout their time period on watch; it must apply from the beginning of the time period in question until it ends.
Because the skill is usually possessed only by fighters, assassins, paladins and rangers, most other character classes cannot employ the ability. It is possible to have a guard as a progenitor, however, and the skill can be acquired through jack-of-all-trades.
Guards who are hired will always have this ability; therefore the party should understand that every trusted guard in the game setting will also have it.