Tom, here, down in the valley. I need to get a photo so y'all can tell us apart. Though my accent usually gives me away....
The survey washers hold up very well to everything but snow-plows. They are available in different colors, materials, and sizes. Survey supply houses can pre-print them, or they can be hand-stamped with a punch.
The roofing washers won't degrade quickly. If they don't get plowed up, could last for years.
Another technique I use for splits is a big nail with survey ribbon on it. You can write the mile down, and drive it flush with the ground. In the grass off to the side of the bikepath, they are hard to spot and won't be molested. If the location is well noted, they should be spotted only if you know where to look. We have traverse all over the county that goes back decades using this method.