Everyone has heard that where a rainbow touches the ground you will find buried treasure. Not many people believe this any more, and science suggests there is no such spot anyway - where a rainbow appears to touch the ground is completely dependent on where you are standing. Leprechauns don't dispute this but say it is missing the point. Which is that in chasing rainbows what matters as much as anything is knowing when you are in the right spot from which to view the rainbow. It depends as much on knowing where you are coming from as where you are going, which requires a particular kind of instinct.
Not many humans have it, so for most of us chasing rainbows is a pretty pointless occupation; but leprechauns, being that much more in tune with the hidden currents of destiny and time and all that kind of thing, are quite often successful. And the advantage of rainbow chasing is that it is a solitary activity, which means the gold does not have to be shared out at the end.
Leprechauns also often use rainbows to mark where they have buried their own treasure, scrambling the signals so that other leprechauns cannot unravel the secret. The treasure they do find is therefore nearly always that buried by humans long ago. Of which there is no shortage in Ireland, where there is still far more treasure beneath the ground than in all the museums of the world. Anyone wishing to bury treasure and not have it taken by leprechauns is advised to plant a hawthorn or whitethorn bush over it. This places the treasure under their protection and they are bound by their own laws to guard it against your return.