My thinking was I would just do a generic knot, but doing further searching it appears the majority have a piece of rope that wraps round part of/all the length of the wall. See images I found with google.

At the end of the day the rope might not even be seen, but I would I to have something there just if i do a scene where one is halfway though being made. So is it best to do it with curves then extrude the geometry down the length of it?