Almost all traditions invoke protection when they cast their circles. This is just common sense, especially if magical work is going to be part of the occasion. In many traditions the protection comes in the form of Watchers and/or Watchtowers that are set in the quarters.
SoulCraft does not do this. Watchtowers in ancient times were literal towers in which guards were posted to look out for approaching people, be they travelers or military forces on the march. While this is an appropriate image for guarding a circle it smacks too much of a military mind-set and seems too aggressive. We recognize that there are unsavory energies and entities that could threaten or interfere with our circles, but we do not subscribe to the paranoid attitude that is necessarily part of the military posture. We do not work with a habitual fear of attack, we simply want to keep our workspace clean and clear of unwanted influences.
The background of the Watchers comes primarily from the Book of Enoch, a pseudepigraphical text that was written in the period between Old and New Testament times. Most of the story of the Watchers is in the first part of the Book of Enoch. There are differences in the details, but a parallel account exists in the Book of Jubilees, an apocryphal book that is not included in most versions of the Bible. The Watchers were originally angels who were appointed to be stewards of the earth and to assist mankind in its development. Some Watchers were involved in creating and maintaining the garden of Eden.
After an undisclosed amount of time, some of the Watchers, led by Semjase, Azazel and Sataneil (spellings vary) began teaching mankind forbidden "sciences of Heaven." These sciences included herbalism and astrology, how to make weapons of war, and how to make and use perfumes and cosmetics. But that was not the sum of these angels' transgressions. They also found themselves attracted to the human women. So they met on a hilltop and entered into a pact to take human wives. The progeny of these forbidden marriages was a race of giants, which in the Hebrew scriptures are called the Nefilim. These giants and their descendants were mutants. They were aggressive and evil, and they either could not or would not control their many insatiable appetites. So they spread war and decimated the land, squandering its resources. They also committed all manner of other atrocities so that eventually the whole world seemed in the grip of unrestrained evil.
Naturally, this ticked off the Supreme Poobah, who pronounced judgment on the fallen angels and sent the Archangels to carry out the judgment. When that was done the Poobah sent The Flood to destroy the evil world and all of the people except for a chosen remnant. While the fallen Watchers were variously imprisoned and made to suffer until the final day of judgment, the spirits of the giants were bound to roam the earth as evil spirits, tempting mankind and wreaking all sorts of havoc, again until Judgment Day.
To be fair, the story does not say that all of the Watchers fell. Presumably there are good Watchers around who are still faithfully doing their appointed thing. Even so, SoulCraft rejects the idea of using Watchers as guardians of our circles. The Watchers (and the Archangels, for that matter) are far older than Christianity or even Judaism. Nevertheless, they are part of a view of the spiritual universe that places it under the authority of a hierarchy of angels, from the lowly "guardian angels" to the Archangels, Cherubim, Seraphim and so on.
This is not part of SoulCraft's view of the multiverse, and we have a hard time understanding how other neo-pagans can subscribe to it.
Some traditions, usually the ceremonially inclined ones, use fixed stars as their guardians. Fomalhauts is usually in the north, Aldebaran in the east, Regulus in the south and Antares in the west. This is a more palatable idea. The problem is that in Babylonian/Assyrian times, when the people noticed that these stars rose almost exactly six hours apart (thus making them natural markers for quartering the sky and being correlated with the directions and seasons), Aldebaran in Taurus was a good marker for the spring equinox. But due to precession this is no longer true. So on a natural level it makes no sense to hang on to a convention that made sense four thousand years ago but no longer applies today.