Link to original: http://sphynxcatvp.nocturna.org/articles/sc-claimspace.html
Help! I've Got an Astral Space Leech!
Whether it's a leech-like psi/astral creature attaching to you, attempted possession or tagalong by psychic/psionic entity, creepy things invading your personal / residential space, or a Working gone wrong (construct creation, etc.)
These, and others, are situations that can happen if you are not cautious enough, or if the attacker is more determined than you are. If it gets to this point, obviously your usual shields weren't up to the task, and it's time to get down to business. You need to drive these things away and the sooner, the better!
Force of Conviction
Remember, true strength comes from within - claim yourself. It's your body, your mind, YOU own YOU, not something else. You have to have 150% certainty about this - do or do not do, there is no try - doubt is bad, because anything less than unconditional certainty gives the entity or creature an opportunity to stay, like saying "maybe".
Now claim the space you're in. It doesn't matter if you rent it, are visiting friends, or actually own the place - it's "yours" while you are in it for the purposes of this exercise. Again, you have to have 150% certainty on this.
Your mind, your body, your space are YOURS - you own them, they are of you. They are filled with your energy and your energy is telling the things that don't belong there to "GO AWAY!" - once you have this conviction mastered, command it to leave. Repeatedly. More forcefully if necessary. Command it to leave until it's gone, and it's only gone when you can't feel it in your space anymore. If you've read the Grounding & Centering 101 article I wrote, you'll already have an idea how to tell what energy is yours.
Now that you've driving the entity or creature away, you need to set up supplemental wards around your space to give yourself a chance to recover and build better shields. If you're familiar with "new age" psychic stuff, you've probably heard of the sage smudging technique many people use. Here's how to do this.
Get white sage - you'll need whole leaves for this, or you can splurge money on a pre-created "smudge stick", that's essentially a bundle of sage leaves tied together with thread, usually somewhat expensive considering the usual cost of the ingredients. The sage leaves you'll typically find in supermarkets are cooking sage, that's different, it'll only work in a pinch if you're really focused. It is said that white sage has a tendency to flare up and spark like crazy around psychic "hot spots", and thus the preference for white sage in situations like this.
Get an old plate, ashtray, or something equally good at withstanding fire. Put the sage on the plate, and light one end of it - can be with a match, lighter, etc. - and let it smolder until there's a strong, thick smoke. (This may not be the best thing for someone still living with their parents, it may smell like marijuana, but if they're open to the idea of the smudge technique, burning it in front of them later should make them realize where the smoke is actually coming from.)
Walk around the perimeter of the space you're protecting, and wave the plate/dish/etc. with the smoking sage in a line next to the walls, across doors, and don't forget bathrooms and cabinets. As you walk (and thus create a smoke trail as you go) reaffirm, out loud if you want, that this is YOUR space, YOU own it, and that nothing that intends harm to you in any shape or form can get in. If you can yell this out without waking people up, this is the time to do it.
Use whatever wording you want, but make sure that you emphasize that it is YOUR space, YOU own it, and always add that nothing that intends harm can come in.
This is a method of focusing your mind to set up the wards around your space. Therefore, if you don't really "get" the whole sage thing, or if more "discretion" is required, you can do it with a stick of incense, a lit candle, even waving around a stuffed teddy bear if it has enough meaning to you. The important thing is that YOU believe this works, it doesn't matter if you do or don't know why.
Based on IRC discussions with the webmaster of Blood & Coffee