The only plant markers I've found that lasted were the thin metal kind that takes an impression of the letters from the pen you use and some I made with my inkjet printer onto Avery address labels. They surprised me a lot since I figured they would be gone in a few months, but put onto the metal labels, they've lasted at least 2 years. I haven't found a pen that will last very long at all. I hope somebody knows of one.

Just dab a clear coat of polyurethane over a label and it'll last. You can buy a small bottle (1.99) in the model paint section. Open it and use a bit of paper towell, swab, napkin or antything else, rub it over dry permament marker ink. Scew lid back on. Takes 5 seconds.

poly sounds easy enough - thanks for the idea -
have you tried it and know it to hold up for years?

china markers/wax pencils are sun and weather proof.

I made a few labels a couple of years ago by using my ink jet printer and Avery labels. I put them on some of the inexpensive metal labels, not copper ones, and they still are bright and legible. I figured the Avery label would be gone by the end of the summer but they've survived for at least 2 years. It was a total surprise to me. I didn't cover the label with anything and they are still sticking to the metal. Live and learn!

Buy a Dymo tape label embosser. The tape adheres great to metal markers and they seem to last many years. Even if they fade eventually (and mine have not), the raised lettering lets you read the label. I use an "Office Mate II 1540 (and use the 1/2 tape).

I put the primary plant name on the front and the variety on the back of the marker.

Use an ordinary school lead pencil when writing on mini blinds cut into strips. It lasts for years!