This is just a small ritual and I have found it works great for me.
You should know that the best protection against negative entities
is the power of a positive and pure attitude during a session.
If you feel that you are stressed or upset avoid doing a session until you feel better.
the protection prayer:
"I am envisioning a bright white light of purity, peace and love starting at the top of my head and working it's way down around my physical
and spiritual body and covering me like a cacoon of goodness. I ask that this light act as a shield to protect me from any negativity or negative
spirits or entities that would try to do me harm. I ask this in the name of the lord Jesus Christ (if you believe) if not you can replace his name with
good and pure spirits."
Then ask your tech/guide spirits to block any negative enrgy or entities from coming through the box. At the end of the session request that any enities
that may have come through the box(you will be reffering to good spirits also) Please return . Give it a few seconds and ask your tech's for conformation 
of their return and the ok to end the session and turn the box off.
that has worked well for me and since I have started to do that ritual I have not had any problems.
Any other help you may need just let me know.
Bruce