What is the best way to draw a border around a viewport?

I have a small viewport, and I would like to know what is the best way to draw a line or border around the viewport.

I tried the following:

  1. I used line renderer and specify the points in 3D. This approach is tedious as I have to specify the x, y, z coordinates to make a rectangle in a way to frame the viewport.
  2. I used Line.MakeRect() method from Vectrosity. It works great. Except that when scaling (switching from 4:3 to 16:9 aspect ratio) occurs, it does not scale but retains position. Which is great, but not desirable as viewport get scaled when aspect ratio changes.

So my question is,

what is the best way to draw a border around viewport? In a way so that it always matches with the scaling effect.

Using Vectrosity, redraw the border if the resolution changes:

import Vectrosity;

private var border : VectorLine;
var borderWidth = 4;
private var screenWidth : int;

function Start () {
	border = new VectorLine("border", new Vector2[5], null, borderWidth, LineType.Continuous, Joins.Weld);
	UpdateBorder();
}

function Update () {
	if (Screen.width != screenWidth) {
		UpdateBorder();
	}
}

function UpdateBorder () {
	VectorLine.SetCamera();
	border.MakeRect (Vector2(borderWidth/2, borderWidth/2),
					Vector2(Screen.width-borderWidth/2, Screen.height-borderWidth/2));
	border.Draw();
	screenWidth = Screen.width;
}