When I was IDing maple trees 3 years ago I used line paint (the stuff for marking ball fields and such) and I can still see those marks today. Very easy to carry a can with you into the woods.
Camp Wokanda
Peoria Park District
2023 - 210 on 3/16 shurflo, sap storage shack w/ 1100 gallon tank - 123 gallons
2022 - 210 on 3/16 shurflo, homemade vac filter & water jacket canner - 104 gallons
2021 - 215 on 3/16 shurflo, added 2nd membrane to RO - 78 gallons
2020 - 210 on 3/16 shurflo, upgraded hp pump on RO - 66 gallons
2019 - 150 on 3/16 shurflo, Deer Run 125 dolly RO - 73 gallons
2018 - 120 on 3/16 shurflo, 2x6 raised flue w/hood, homemade arch w/ AUF & AOF - 34.5 gallons