Anchors are a great solution to retain unstable rock and earth.  Basically and anchor is a tendon installed through an unstable structure into a stable competent structure.  The anchor can be passive or active which means it can be under tension or not under tension.  If placed under tension, the anchor is pulling the unstable portion of the structure back into the competent material not allowing it to move what-so-ever.  If it is not under tension it is often referred to as dowel and it acts primarily through the shear strength of the tendon.  Anchors tendons can be made out of many types of material including steel threadbar, cable, fiberglass and other components.  The anchors are normally secured to the structures with the use of cementitious grouts, chemical epoxies, resin or mechanical wedge anchors.  Anchors can be uses in almost any substrate from rock, silt, sands and gravels.  We at Norpac have extensive knowledge on all types of anchor installations and can provide solutions to any of your project needs.