Always a problem. Tags get lost or mixed up. I noticed on the daylily forum some conversation about this problem, especially things that will stay in the same pot for a long time. I wanted to post here though so everyone that wanted to could try this.
I have found that china pencils, also called grease pencils, work very well and never seem to come off. They come in different colors so can be used on any color pot.
We tried stapling the tags to the pots but the tags eventually broke off so that didn't work too well for us.