Get some lite climbing rope or parachute cord  

[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/Hy6CL.jpg

You pass the rope loop through the ring the pass across the bottom and up the top side.   
It is called a Lark's head (cow hitch).  

And I would use fisherman not on the rope.  I think that is what you are currently using.