Watchmen on the wall is a lot like the "watchman on the tower" parable, in which because the watchman is higher up and is looking out, he can see the enemy approaching long before the ground troops can. He sees a danger coming that they can't, but they trust in the watchman's eyes and judgment enough to arm themselves and get ready for the upcoming battle.
Ron Paul is definitely a watchman on the tower, seeing the dangers coming long before others could.
"Moderation in temper is always a virtue; but moderation in principle is always a vice." -- Thomas Paine