Only had to use this one once but its a goodie.
There is a micro cache in the Southamton City Centre Parks. Shoppers pass with in feet of it every minute. So we hunted for it for best part of an hour, with out a result, because we just couldnt get stuck in.
We came back the next day, but this time my son aged 4 held in his hand......
Wait for it ....... a Tennis Racket with the rehearsed phrase 'have you found the ball yet dad'
Cache found in minutes. Try it, it works wonders.