With Norse raids on Christian monasteries in the late 8th through early 11th centuries being so common, were defense forces of any kind appointed to guard them? Monasteries in Ireland Scotland and England are usually depicted as helpless sitting duck targets, but is this accurate?
In short answer, "Completely", almost probably no, but "relatively" would be more accurate.
As I illustrated before in: Is there any record of "Conscientious Objectors" from the Viking Age?, 9th century Western Europe (Continent and the British Isles) were generally far more violent society than generally assumed, and it was not uncommon for some Irish church/ monasteries to have some armies (for fighting each other).
Unfortunately, they were sometimes also so politically divided that even some of them "hired/ instigated" the Vikings to attack their rival(s).