It happens more than you think.
The best bets for OM are probably #2 and #8.
Hey Sven, my buddy (and 18 handicap) Peter lost a ball on OM #2 short right while out there for the Kings Putter--the earth swallowed it up as it was pretty wet over there...
Since I've lost balls in the middle of dry fairways before (particularly, it seems, in Ireland, where it must be the leprechauns), I think the answer to this question is "None."