From ‘Psychic Self-Defense’, by Dion Fortune

The Christ-force is the equilibriating, compensating, healing, redeeming, purifying factor of the universe.  It should be invoked in every operation of psychic self-defense where any human element, incarnate or discarnate, is concerned. Where non-human elements, such as elementals, or thought-forms,  have to be dealt with, it is the power of God the Father, as Creator of the universe, that is invoked, His supremacy over all the kingdoms of nature, visible and invisible, being affirmed.

To seal the aura: 

Stand upright and cross yourself, by touching forehead, breast, right shoulder and left shoulder, saying, "By the power of the Christ of God within me, whom I serve with all my heart and with all my soul and with all my strength (extend your hands forward as far as you can reach at the level of the solar plexus, finger tips touching, then sweep them round to the back and touch the finger-tips together again behind you, saying), I encompass myself about with the Divine Circle of His protection, across which no mortal error dares to set its foot." This is an old monkish formula. It is very effectual, but its potency only lasts about four hours.

There are various other devices which are useful, should you meet with any unwanted influence:

If you have to interview persons whose influence you find overwhelming, imagine that they are separated from you by a sheet of plate-glass. You can see them, and hear them, but their magnetism cannot reach you. Visualise this sheet of glass until it appears to you to be absolutely tangible. 

If you have to associate with persons who distress you, but are not actually interviewing them, imagine that they are separated from you by a brick wall, and say to yourself, "You just aren't there. I can't see you or hear you, and you simply don't exist."  

When dealing with a person who saps your vitality, interlace your fingers, and lay your folded hands upon your solar plexus, keeping your elbows pressed against your sides. Keep your feet touching each other. You have thus contacted all your own terminals and made of your body a closed circuit. No magnetism will go out from you while you maintain this attitude. Your friend will probably complain of your lack of sympathy, however kindly you may speak.