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I haven't heard the particulars of this technique of the saints, but I suppose it might entail getting the permission of the subject to let you place the rosary over his head, otherwise you'd be risking a fight breaking out. Like if you tried to do that with any of the growing number of publicly professing satanists these days, it would probably come to no good.
Even a protestant so-called evangelical would likely fume and scoff at such an idea, forbidding you to come near with your rosary.
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But then againin the case of a person who is truly possessed by the devil, when the devil realizes that the person is under the special protection of the Holy Virgin will depart on his own because it is unable to remain in the presence of the special holiness that is the Holy Virgin. It would not matter whether the person was a Protestant or had been a Satanist. The Holy Virgin is the mother of us all.