Hi Peter,
Tagging with long lived tags is not a trivial problem. Metal tags of type or style noted by
@vp999 being one sided work well, or well enough. I at one time used brass "coin shaped tags, with numbers", got 2 of each, one was tied to tree one was buried in the pot with the roots. The double tag was because just often enough a tag would fall off or get pulled off or knocked by bird or human. The tag buried in the pot was the "emergency" backup ID.
The number was then used on an inventory list on the old laptop. The numbered inventory got abandoned when I began to feel I was spending more time creating records, or inventory notes about my plants (orchids and bonsai) than growing orchids and bonsai. Where do you put your energy when time is short? Now that I'm retired, time isn't as pressing an issue, but I still resent time spent record keeping when I could be "correcting people who are wrong on the internet" just joking.
I found that the best for convenience is the plastic white plant tag and writing with a number 2 pencil. A pencil will slowly fade, but even when quite faded, there will be faint traces and usually scratch mark in the plastic you can read, even if difficult. Markers and ink pens tend to be fugitive, you can read them one day, then poof, they are faded so completely that nothing can be made out. Because markers are more like paint they don't leave the scratch mark in the plastic plant tag that a pencil does. Orchids, where provenance means price difference of hundreds of dollars, tagging is important, and for my money the plastic plant tag, and pencil are the way to go. I do often, for my "important plants" take a second plastic plant tag, break it in half so it is small enough to fit, and bury it in the pot, in the roots of the plant, not visible. Then if a squirrel or a two legged critter pulls the tag out of my pot, I can still recover the provenance when I repot the orchid or tree.
I had a visitor once who was nearly blind, he pulled the tag out of every plant he looked at in order to read the tag. He stuck the tag back, often in the plant next to or near by the original plant. It took me a year to straighten out the labelling of my orchids. I became less willing to have visitors. Fortunately I had already begun the practice of burying an extra tag in the pot. Once the repotting cycle was done, my labels were back in order.
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