A member of my local Facebook group brought up hula hoe in a recent post. I wasn't familiar with the tool. Time I found out! Surfed the net a bit and came up several designs, a wide range of prices and lots of ideas. The designs were pretty straight forward, but a bit time consuming to make a functional tool. There must be something just as effective one could make on the fly with stuff lying around.
Found a gentlemen on You Tube using small loops made from bandsaw blades connected to a pole to make his weeder. Seemed to work well, however the saw blade serrations tended to collect weed debris at times. Didn't think I'd wanna buy a bandsaw blade if there was another material just as effective and readily available.
I do a lot of work with sheet metal. Plenty of scarps floating around. I cut a 20 cm by 3 cm strip out out of .5mm sheet metal. Made a loop and attached the loop to a length of wood 3 cm by 5 cm with old bicycle inner tube. I've since made another type from coffee cans. Takes advantage of the circular shape already present.