Or maybe then a plastic yardstick or a aluminum one. You can always highlight in red paint at certain intervals. What worked out nice for me is I made my red marks all the way around the pipe so you could read it from anywhere on the pond. Your 2 foot fluctuations should be very easy to keep up with. Good luck.

Dear Alcohol, We had a deal where you would make me funnier, smarter, and a better dancer... I saw the video... We need to talk.