It's been a while, but years ago when I was working for UP I saw a brakeman take a step backward on a flat car deck and step down to his knee in a hole on the deck.  He wound up with a slight sprain and got so much ribbing he even refused to take a day off, just limped along for a couple of days.  The hole was around a foot in a semi trapezoid shape and there were a number of spots that had smaller holes or chunks out of them.  The car was about 3-1/2 years old as I recall, nice clean sides but the deck looked like a test platform for a nuke.  As I recall the deck was greyed out mostly but a few of the spots had more natural wood color to them, just hadn't been around long enough to grey out.  To add to the modeling, there were a couple of pieces of chain attached to bolts that ran through the deck where something had been chained down and the chains just left behind, a few nails sticking up and general debris where it hadn't blown off yet.  Probably too disgusting looking to put on a layout :)

John Larkin