We have a fun game with my in-laws.  One year, over the holidays, my mother-in-law secretly placed a motorcycle-riding gnome in our yard before departure.  We found this to return the favor!  Strategically situating underneath some outside stairs, we had bets placed as to when it would be discovered.  Husband won (@ "less than a week"). It's provided its weight in gold for all the laughs it has produced.  Mom-in-law declared it's going to be a garden centerpiece!  LOL.  She also said, "It's war!"  Will try to keep you updated as to what happens next!