I would like to disagree. I imagine the Boozons (dwarves) as particles of the Fortion (Fortress, derivative of the Fermion [Yes I know it's the class of particles that contains Bosons, but it works

]) and that the Fortion emits a "magnetic" field of a set size at the beginning of the Fortion's lifespan. The Fortion cannot grow to beyond this size, but can occupy all of it or very little and still manage to exert this field around itself. This field allows all dwarves to observe all things the dwarves have already seen within this field, but anything that leaves this field is no longer under affect of this field, and therefore unobservable.
Animals, for instance, once they enter the field upon an observed piece of land, become instantly acknowledged by all Boozons as existing, though it may not be in direct view of any Boozon. Goblins and necromancers offer a special challenge, but I think it's solveable easily enough, as they exhibit "Anti-Boozon" qualities, such that they are able to enter the Fortion's field of effect undetected, and, when spotted by a Boozon, collide with it in a very energetic and destructive manner. I shall therefore refer to Goblins, Necromancers and similar creatures able to hide as particles of the "Anti-Boozon" class.