I have a little 1"x2"x6.5' red oak board that I am using for a measuring stick to record my kids' heights every 6 months. I make a notch for their height with a chisel, but I would like to write their age next to the notch. I am using a pencil now, but I would rather have a permanent ink. Is there a better option than a sharpie? I don't want it to smear or fade over the next 20 years or so.