Circles and ?

In creating safe sacred space, it has been traditional to cast a circle of three concentric rings. These circles serve to protect the people within them from any malevolent influences that might be near.
When we founded the School of Wicca, we were puzzled by references to circles of various sizes: diameters of 9 feet and 11 feet were popular. So we decided we would ask students of the School (who by and large had not been exposed to the texts, whether ancient or contemporary) to cast circles of various sizes in order to decide which worked the best in a modern setting. The test was simple: Cast a circle. See whether you could (a) feel any negative influences while you were inside it and (b) send information to a third party from within it. We chose the idea of sending love or red roses to a friend.
After casting many circles in many different materials and of many different dimensions, we decided that the best materials were those that were electrically conducting. They could be anything from heavy copper tubing, to coal (that is, carbon), to sulfur, to salt that had been dampened, and copper sulfate. We simply chose three of them for our circles, basically because the colors of the materials seemed to match the idea behind the specific circle being cast. Thus for an outer protective circle, we used sulfur. For a circle on a higher plane we used bright blue copper sulfate, and for the healing protective circle we used salt. The sizes of the circles were difficult to pin down but finally realization came through that the outermost circle must be indivisible; i.e., the circumference must be a prime number. Working this back to the diameter, we found much to our surprise that the number had been well known when the ancients built their stone (megalithic) circles. So for many years, using only a piece of string and a pivot in the center, we could cast our triple circle with ease. We had to be careful of the copper sulfate, though; because if people had cuts on their feet, it might cause them problems: copper sulfate is a poison.
Recently we've been trying to figure out a slightly different arrangement: One of our students noted that the stone circles are not accurate circles: They are in fact closer to an ellipse. Casting ellipses is not all that difficult--and the big advantage is that they have two focal points. An elliptical shape provides a location for the priest (flamen) and for the priestess (flamenca), allowing a balance that had not been available in the single center point of a true circle.
If this was not enough, it has recently been pointed out that instead of an ellipse, it might be better to think of two parabolas facing each other. The advantage of this arrangement is that energy from the one focus would be transmitted to the other and thus could be multiplied. Casting parabolas is quite tricky. You will have to go back to your high school geometry book to figure out how to do it. We would very much like some of you more dedicated workers to try it and tell us about your experience.
For more information on casting of basic circles and ellipses, you can refer to Appendix III of the Solitary Wiccan's Bible by Frost and Frost, Samuel Weiser. York Beach, ME