Let me amend the words of the version I know from this enlightening information from another site, showing it may well have been Finn and not fens:

- "Historic Fords of the Finn"
The Wild Raparee Priest

On the bleak hill of Gadra, where the winds howl
He creeps to his hiding place among the wild fowl.
No cry greets his advent, their comrade is he,
And they dream of no harm from the wild Raparee.

But who be those horsemen so late in the storm?
And what seems that glare, tis the king's uniform.
God grant that awake and not sleeping he be,
They are on the track of the wild Raparee.

Tis morn, and the horsemen return from the heath.
But the sword of the foremost is not in it's sheath.
Ah no, on it's bright point, all glory to see
Is the head of the outlaw, the wild Raparee.

James McLaughlin
Written of a priest who sought safety on the high lands overlooking the Finn Valley