(This is a post from a recent thread. I though it was worth repeating here for easier referencing.
Safety knots work wonders!
You may have already learned this, but here it is again.
Place slip knots in your down rope as you ascend. They have to be oriented the right way. After tying the slipknot grab it and pull on the side coming from your climbing hitch. It should hold.
It should be able to be pulled loose when pulled from below.
Having these knots in your down rope prevents you from being able to descend passed the knot until it is removed. As you descend the hand controlling your descent will be on your down rope. when your hand hits a knot, stop. Remove your hand from the climbing hitch and use that hand to pull from below the knot and remove it. You can replace your hand on to your climbing knot and continue to descend. Your braking hand never has to leave the down rope.
Descending is one of the more dangerous aspects of tree climbing and safety knots are a well proven method of managing that risk.
A safety knot is not just useful as a "safety net" in DRT climbing. A climber can place one anytime he needs to provide extra security if a given system has the potential to slip.
Just remember it is VERY IMPORTANT
to have the knot oriented the proper way. If it is tied backwards it serves no purpose