I will look for the industrial sharpies, but so far, every pen (even oil paint pens) eventually fades in my hot, humid climate. I also use vinyl blind slats for markers and they work great, but I found a Brother brand label maker on sale for about $10 a few years ago and made the investment. I am amazed at how well the labels hold up! I've not had one of them fade or tear in the last few years since I started using them. The label tape can be kind of expensive (about $15 - $20 for about 60 ft), but I look for the off colors that no one else wants (pink, lime green, etc.) which are often on sale at reduced prices. The label tape is probably less expensive online, but every time I run out, I just rush out to the nearest office products store and buy more. You know how it is when you just gotta stick a label on a plant or propagation experiment before you forget completely what it is. LOL
Jeremy