I use an adjustable friction saver. Just make sure that the rings don't touch each other. In other words, if you're on a 5 inch spar, shorten the friction saver down to about 4 inches. That also helps the angle of the rope by making it two 90 degree angles instead of one 180 degree angle. If you have a standard friction saver, cross it over itself on the spar at least once so it doesn't slide down. Or as BC WetCoast says, use a bowline and an 8. If you use a running bowline, and you leave a long tail on it, and if there are no limbs on the spar, you can rappel down the rope to your next cut, lanyard in, pull the tail to bring the bowline down, then re set it and start over. Assuming you have dropped the top and are blocking it down.