Writing on the back of photos

I like to date my family photos (by writing the date on the back). I'm just wondering what the best way to do this is. I've tried a few things: Pencil doesn't work, I had a date stamp but that would smear off onto other photos. Is there a best way to do this? I assume permanent marker would eventually show up on the image side when the images age.

Any advice is greatly appreciated

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Chris
http://s1215.photobucket.com/home/Albino_BlacMan/index