I got a cheap punch set and a few round blanks. I attach variety and year on one side and a number on the other. I catalog various info about each tree on an excel file corresponding to the number, but like having the variety and year on the tree itself. I attach using arbor guard tree lock (the heavy duty, plastic, hook and loop style ties often used for attaching the tree to the stake) along with either a zip tie or key ring.
I attach to the lowest scaffold branch at the trunk with plenty of wiggle room.
It works really well and should outlast me.