battlements, battlemented walls
堠 centers on defensive fortifications: battlements and battlemented walls, the notched parapets used for protection in military architecture.
堠 combines 土 (earth) with 侯, which likely contributes the sound. The earth radical suggests earthen fortifications, fitting the meaning of battlements.
The left side is earth 土, and the right side 侯 resembles a watchtower with notches. Picture earthen walls with lookout points: 堠 are battlements.
For コウ, imagine a soldier calling out 'Go!' from the battlemented wall: Go -> コウ, as they defend the fortification.