Here's your shield against those:
Psalm 101:
1 I will sing to thee, O Lord, of mercy and judgment; I will sing a psalm, 2 and I will be wise in a blameless way. When wilt thou come to me? I walked in the innocence of my heart, in the midst of my house*. 3 I have not set before mine eyes any unlawful thing; I have hated transgressors. 4 A perverse heart has not cleaved to me; I have not known an evil man, forasmuch as he turns away from me. 5 Him that privily speaks against his neighbour, him have I driven from me: he that is proud in look and insatiable in heart,-- with him I have not eaten. 6 Mine eyes shall be upon the faithful of the land, that they may dwell with me: he that walked in a perfect way, the same ministered to me. 7 The proud doer dwelt not in the midst of my house; the unjust speaker prospered not in my sight. 8 Early** did I slay all the sinners of the land*, that I might destroy out of the city* of the Lord all that work iniquity.
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* Your house, your land and your city is your heart. Those who speak evil thereat are the demons, whether they use men to do so or directly through our thoughts.
** Early means the minute you detect an evil thought you should resist it by calling upon Christ and recalling appropriate verses from scripture.