This knot will work on a rectangular shaped rod too. I chose to do it on a 1/2 inch thick steel throwing spike I made. A clove hitch is a great knot, it's a required Boy Scout knot and it the base for many lashings. Sorry about the shadows.
You could use any type of string but I'm using a scrap piece of paracord. First you take the string and drape it over the object
You'll then need to bring the one end of the string back under the object
You then take the end of the string you brought back to you over the other string and make them cross.(The photos explain it better)
You now need touring the end if the string so both lines are the same direction
You then bring the end that you've been moving through the center of it
Then pull it tight and your done! Feel free to comment and/or follow me.