Final answer:
Jack's tribe's specific weaponry for defending Castle Rock is not detailed, but they likely use a combination of spears and natural fortifications, drawing from historical examples of citadel defenses.
Step-by-step explanation:
The weapon that Jack's tribe uses to protect the entrance of Castle Rock is not explicitly stated in the descriptions provided.
However, from the various examples given such as men carrying shields and spears, the concept of gate guardians like the Man-Headed Lions or Lamassu, and references to traditional defenses like moats and castle walls, one can infer that Jack's tribe likely employs a combination of defensive features of Castle Rock to secure the entrance.
In historical contexts, the entrance to a citadel would often be heavily fortified, as seen in the description of the Lion Gate, with its creating a tunneling effect that deters invaders. Thus, Jack's tribe may similarly rely on both weaponry and the strategic advantage of terrain to protect themselves from external threats.