Masses of Irish stuff was destroyed in the 1970s or there abouts in County Louth. Bits keep turning up, re-used in souterrains etc. There's a load in Wicklow that's waiting to be rediscovered. I have rough directions to some of it. Some Wicklow based stuff has also been destroyed recently.
Rock art seems to have been a taboo in Ireland at some point, as much of it has been buried or blown up.