I was skeptical about this at first, but I heard that saying "I break all contracts with negative entities" or something along those lines works.

I had a few chances to try this over the past couple of weeks, and it certainly does work. Very powerful actually. I had some kind of negative alien attached to my lower back last night and it was sending me into spasms with lots of negative energy. I said "I break all contracts with negative entities" and it immediately faded away.

It works on the principle that these beings actually apparently can't violate free will and that at some point we've made a contract with them that they can use us in this way.