Only thing that lasts in my central Oklahoma summers is china markers, pencil, or the pen that ranchers use to mark cattle. Everything else wears out in a few weeks.

Two things I do with my mini-blind tags:
1. In the winter slow time, I list all the tags I expect I'll need and what info needs to be on them. Then I print out laser printer waterproof labels with that info, and stick them on the tags, ready to be deployed when needed. These never fade, can be reused for years, and if I drop a variety, I can just cover up the old tag with a new one. I've got some tags that are at least ten years old now.
2. I put them out with paper clips. On trellised crops, the tag gets clipped to the trellis. For other crops, I use those surveying flags on wires. I roll up the flag part before clipping the tag on, so the wind is less likely to flip the tag off, and just clip the tag on.
Also, a large paper clip with the big leg straightened can hold a miniblind tag with just the straightened leg stuck into the soil. I do that for tagging my soil blocks, especially for market sales of starts.

I find if I place my labels to face north, the marks last all season.