fades a black marker, too. Red fades faster, though.

Maybe get one of those oldstyle label-makers that pressed the letters into a strip of plastic?

So that you essentially 'engrave' your labels into the copper on the marker.

(Edit: You have to use a hard stylus to press in, obviously.)

I've tried scratching on the inner side of Coke cans but that's hard to see.

The Central Florida sun and rain will make quick work of Sharpie ink.