(i) Wall

(ii) Two hebrew words are used...

(1) Kothel (3796)) - from an unused root meaning to compact; a wall (as gathering inmates):

(2) Chowmah (2346) - feminine active participle of an unused root apparently meaning to join; a wall of protection:

A thick, high, continuous structure of stones or brick that formed a defensive barricade around an ancient city.

The walls of public buildings and royal palaces were often made of squared stone blocks, cut by skilled craftsmen and carefully fitted together. Solomon employed 80,000 workmen to cut and place the stones for the Temple in Jerusalem <1 Kin. 5:15>.

(from Nelson's Illustrated Bible Dictionary)

(Copyright (C) 1986, Thomas Nelson Publishers)

(iii) (1) Boundaries of our own comfort zones.

(2) Protective boundaries of God (Walls of Salvation) / Spiritual Leader

(iv) (1) (a) 2:9

(b) Prov 18:11

(2) (a) 5:7; 8:9,10

(b) Isa 26:1, Isa 62:6