Don work gloves. Cut the rubber shielding around the wire a few inches from one end using a utility knife. Cut all the way through the rubber shielding down to the metal core of the wire around the full circumference of the wire. Once the cut has been made, pull the rubber shielding off the end of the wire.
Tie this bare end of the wire around a pole, tree or other fixed point. Angle the edge of the knife toward you, resting it on top of the bare wire at a 45-degree angle into the wire at the edge of the shielding you cut. The core of the wire being metal prevents the blade of the knife cutting straight through, and acts as a guide, allowing you to cut the shielding without cutting the wire.
Walk backward, pulling on the wire with one hand, with your other hand holding the knife against the wire. As you walk backward, the knife follows the core of the wire, cutting and removing the sheath. Continue walking backward as far as you need to to remove the required amount of sheath. After you finish cutting the casing, pull off any excess that remains from the wire.