>How would you tell if it failed? The victim would remained possessed by demons? --jks
What if the demon was Jewish? Would it respond to a catholic pope?
I mean, you have to figure if there is so much splintering of religions in the physical world - why can't it be just as bad in the ethereal plane? Maybe that would explain why you never hear of possessions by some Demons - they are kind of like the switzerland of religions - refusing to get involved.