The Derry Down combination in choruses goes back at least to Tudor times and is and has been extremely common for centuries. Dana, you seem to be suggesting that 'derry down' is Celtic. The doe is also used metaphorically in other 17thc songs. 'Check out 'The Keeper'. (also a derry down chorus) but in that it is used as a sexual metaphor, still for female humans. I must follow up this reference to 'Derry Down' as a place, albeit mythical. If Derry in Ireland does indeed have a 'Down' that predates Tudor Times that would be of great interest.