[aredox]

No, what is means is that at the location, the stand-in for the golden owl was rusted.

The creator of treasure hunt didn't bury the actual golden owl, to keep the artwork clean and to force the finder to reveal that he/she has indeed solved the puzzle, and not just stumbled upon it.

[kulahan]

Isn't gold pretty much the one thing you wouldn't need to worry about keeping clean if you buried it?

[aredox]

From corrosion yes. From dents and scratches, no, it is pretty soft.

And even then, there is a caveat, as gold can superficially corrode and change color under some anoxic conditions (as some people who put gold jewellry in safe boxes discovered).