[tguvot]

do you have sharpie that won't grind down to zero on concrete after 3ft ?

[tomovo]

Not on genuine HP concrete.

[tguvot]

Hp concrete actually exists

[rpcope1]

Hopefully they're using something like a paint pen with a roller and not a Sharpie the way you're thinking of it.

[tguvot]

parent is the one who suggested sharpies.

i'll actually bet on some variety of inkjet/spray as it will better deal with surface imperfections and won't wear out