See the following message I posted previosly:

I want to tell everybody on the forum about what I feel is the best system out there as far as safety is concerned. I saw this first in a video I got with a Gorilla treestand this year and also talked to an NBEF instructor who uses it. It uses a climbing rope and a knot called a "Prusik" knot.

You tie the rope arount the tree at a height above your stand and leave enough rope to hang to nearly the ground. You attach the prusik knot to the rope and then attach your harnes to the prusik knot using a carabiner. The knot can be easily slid up the rope ahead of you as you climb and slid down with you as you descend but will grip the rope under a load and will not slip. This system allows you to be connected to a safety line 100% from the time you leave the ground until the time you return.

Of course you need to use some other system on the initial climb before the rope is tied but this system is truly the easiest and safest I have seen. Anyone interested in learning details can simply visit any shop that specializes in climbing gear as this knot is fairly widely used by climbers.