It took me about 3 visits to find this stone. Finally I asked in Cahir Castle about whether it had possibly moved into the Castle.
The girl behind the desk didnt know but there were two OPW workers hanging about and one of the guys could confirm it was there. He called it St Patricks Knee stone.
I headed back up again and used a stick on the over-growth around it. Im living in Cahir at the moment so will try and keep it clear of growth.