How do you ventilate a parapet wall?

Consider the following for venting a parapet wall.

It's possible gable louvers could work. They resist bird nesting, and due to the angle they would have a very low probability of weather infiltration. However, venting parapet walls means that some of the louvers will be relied upon as intake vents and others as exhaust. Controlling which ones do what is nearly impossible and may not function as intended. Please consider an internet search for additional options.