Henka raised an interesting point in another thread: what is the nature of protection when doing inner work.
I recall a friend in my youth who used to surround his girl friend with light to stop her getting pregnant. I did not understand the logic - and his approach did not seem to work very well.
In a Masonic lodge we say we tyle the lodge and use an Inner Guard armed with an steel blade but we rarely instruct on any but the physical work.
So what are the various means of spiritual protection?
What are the preconditions for them to be effective?
That depends. In my community, it is practiced as a matter of course.
They say Japan was made by a sword. They say the old gods dipped a coral blade into the ocean, and when they pulled it out four perfect drops fell back into the sea, and those drops became the islands of Japan. I say, Japan was made by a handful of brave men. Warriors, willing to give their lives for what seems to have become a forgotten word: honor. -The Last Samurai
There are different levels. On a personal level, we use a "bubble" around us to reflect negative energy away. This is achieved through visualization. In a group setting, when we cast a circle (which is more a bubble), we call on the elementals of the directions to empower and guard, as well as invite the Lord and Lady to attend. We ground and center beforehand, sinking our roots deep into the earth and drawing that energy upward, and drawing the sky energy downwards until they blend in our center.
I have a crystal matrix in place at home, consisting of a crystal at each cardinal direction tied to a master Quartz on the pentacle on my altar, empowered by my patron deity, Lilith.
They say Japan was made by a sword. They say the old gods dipped a coral blade into the ocean, and when they pulled it out four perfect drops fell back into the sea, and those drops became the islands of Japan. I say, Japan was made by a handful of brave men. Warriors, willing to give their lives for what seems to have become a forgotten word: honor. -The Last Samurai
One interesting aspect of group protection (tyling) is that the presence inside the group or protected area of a person carrying adverse energies or intent is that the protection is largely nullified.
I recall a housemate who complained of possession. While I was able to displace the entity it immediately returned because the housemate was holding a form of negativity.