This is my xylophone visual that I use whenever I'm teaching an orffestration. If we are setting up in pentatonic I have black slips of paper that I place over the bars that need to be removed. I've never really had anything that worked for indicating the bars for a bordun. Today, spur of the moment, I grabbed a couple of magnets that I had at the front of the room and stuck them above the bars we were using.
What a life saver!!! I never once had to repeat it. I saw many students reference the visual when they rotated to the bass part but I didn't have to waste time saying it. Don't you just love those magical moments when you do something smart!!!