Safety harness or not, it is, and always will be, one hand for yourself and one for the ship. Safety harnesses usually work, but nor always. But, what they almost always do is give you a false sense of security. I have rock climbed in Yosemite, done roofing on multi-story dwelling units and trimmed very tall tees. I also always made my own harnesses if possible. You NEVER put your life in the hands of others if you can avoid it.