It's a bit wordier than I originally intended, but I came up with the following:
A gray sqaarg is a golem like construct whose stocky humanoid form stands 5 feet tall. It appears to be crudely moulded out of clay but is actually made of solid stone. The creature is sculpted in the shape of naked sexless figure, bald and completely hairless, with broad shoulders and a heavily muscled physique that resembles an oversized beardless dwarf.
Gray sqaargs are capable of self-repair and effectively heal as quickly as a living dwarf.
Dwarven Guardians. Gray sqaargs were created by a long extinct dwarf dwarf culture. The objects and writings of these dwarves include unmistakable proof that they were evil creatures, who scholars speculate might be ancestors or relatives of the Duergar. Despite their creators' malevolence, the gray sqaargs are protective creatures designed to guard the territory and property of the dwarves by capturing intruders nonlethally.
There are unverified reports of more types of sqaarg than the grays, with other colors of sqaarg performing different functions in the ancient dwarf society: white sqaarg acted as heavy laborers, red sqaarg were deadly warriors, and so on.
A gray sqaarg is technically nearly mindless but capable of following complex instructions. Gray sqaargs are assigned a "beat" to patrol, such as the entrance to a mine and its surrounding paths. If it encounters a creature it wasn't told to let pass, which may requires a password forgotten centuries ago, the sqaarg tries to capture the intruder. It then imprisons the intruder and awaits orders from a dwarf master, who are unfortunately all long dead. Captured intruders must thus escape or eventually die of hunger, thirst, or old age: the sqaargs rarely have instructions to give prisoners food or water and are tireless and unaging jailers. If an intruder fights back, the sqaarg uses the "Knocking a Creature Out" rule and tries to render its opponent unconscious. A gray sqaarg only uses lethal force as a final option triggered by preset conditions, such as after being heavily damaged (e.g. at 35 hit points or less) or if the intruder stole a sacred dwarven relic.