Here is the version Karan Casey recorded on her CD "The Winds Begin To Sing", which is most likely the one you heard:

WHO PUT THE BLOOD (Trad.)

Where have you been all the long summer's day
Son tell it unto me
A-fishing and a-fowling in the fields and in the forest
I am weary mother let me be (repeat last line)

Who put the blood on your right shoulder
Son tell it unto me
It's the blood of a hare that I killed yesterday
I killed most manfully

The blood of a hare it would never be so red
Son tell it unto me
It's the blood of a boy that I killed yesterday
I'm weary mother let me be

What was between yourself and the boy
Son tell it unto me
It was mostly the cutting of a rod
That never would come to a tree

What will you do when your father finds out
Son tell it unto me
I will put my foot on board a ship and sail away
And sail to a foreign country

What will you do with your lovely wedded wife
Son tell it unto me
She can put her foot on board a ship and follow me
And follow after me

What will you do with your two fine babes
Son tell it unto me
I'll give one to my father and the other to my mother
To keep them company

What will you do with your house and lands
Son tell it unto me
I will lay them bare to the birds and the air
There's no more welcome for me

What will you do in the winter of your life
Son tell it unto me
Like a sally in the rock I will bend with the wind
And pray for the gods' mercy

Hope this helps.

Cheers,
Michael