Easy. Stop believing it happens.
Or, if you are not able to do that, there are two visualizations you can use.
(1) envision a glowing translucent "shell" around you (like an eggshell around your entire body), through which no unwanted energies can pass. There is a variation on this, where you lie in bed at night and envision a "fence" of glowing light around your property, along the property line.
(2) the other visualization is to imagine a screen between you and this person, and everything they send your way hits the screen and falls down to the ground where it cannot reach you.
It doesn't matter if these visualizations DO anything. All you need to do is convince your subconscious that they are up and working .. our subconscious consumes whatever we feed into it.
Including the fear that we are being psychically intruded on.
With all visualizations, the more you focus and concentrate on the visualization, and the longer you do it, the more effective it will be ..whether it is actually affecting unseen forces or merely programming your subconscious (we cannot tell which it is, but it will be effective if properly done).