If it were me and I was set on doing this myself, I'd follow Pat B's advice and method. I used to rock climb and those folks know how to keep from falling to your death or worse, disability.
That being said, I wouldn't even do that. I'm a DIY guy and basically as cheap as they come. But for the few extra bucks you pay for the commercial, tested, designed products, I'd just buy this stuff pre-made. The folks with the liability are going to do it right in our overly litigious society.