To me the cork and kerry mountains makes a lot of sense. The highest mountain in cork is very close to the Kerry border and the area is pretty much inaccessible, apart from foot and sure footed horse/pony. From Glengarrif to Kenmare over the Priests leap is fairly wild country and the alternative road to Kilgarven was built during the famine as a job creation scheme well after the song was created. Further east the countryside is equally rugged towards Gougane barra. The area provided thousands of acres to hide out. Even today sheep farming in the area provides a challenge accessing certain of the commonages.(I speak from personal experience.There are a lot of bogs and cliff faces and even a quad bike is of limited use)