User blog comment:Daftpunkbro/Hookedon Harry Potter Series/@comment-68.226.202.135-20120129163812

Dementors are not flesh-and-blood creatures; they are not truly alive, either. One cannot - even with really powerful advanced magic - kill something that doesn't truly live. Dementors can be repelled by a Patronus (an extremely powerful Shield Charm fueled a happy memory or thought), however.