There are lots of ways that you can make it very difficult to find the transmitter, often
unintentionally. For one hunt I did the transmitter was wedged in the bottom of a coffee
cup, upside down on the table. At least one hunter picked up the cup and looked underneath,
but didn't turn the cup over and look inside it.
I've also seen the transmitter that was put in a bikini top...
But in my experience, making the transmitter too difficult to find is counterproductive, because
people get discouraged when they can't find it. Better to put out something that isn't too
difficult to find, then keep re-hiding it as needed. Once people get the confidence to find it
you can make the hiding places more challenging, as long as they can still find it sometimes.