Dear Featherpoint,
Make it clear that they are not wanted nor do they have permission to enter that space. ( We may unintentionally open ourselves up or develop a rapport that allows this intrusion, so it is essential to establish that this is not OK). Visualize a protective field seperating you from the intrusion. If the intrusion continues despite your efforts, visualize the cord that connects you & cut it with a sword or flame, etc.... Request help from those you consider your protectors ( God? Angels? etc) if needed.
Many people in different religous faiths gaze
upon the image of a spiritual person, protector or deity daily and repeat their name in mantra or prayer. Over time,when in need the name will escape the lips as easily as the breath. Feeling a connection to a protector is of benefit.
Salt water baths, meditation on love & compassion,sageing the room & self, etc.
Not sure if this is considered basic protection by your friend, so I may not be adding anything to what has already been attempted. :)
peace & joy,
holobon