Paul is right, the USFS would not allow a metal cable being strung across the creek at DCHS. They would take something like that down for sure. For one thing, there are to many liability issues associated with a permanent fixture like your suggesting. Someone did afix a metal plate onto the granite across the creek from the hotpools and they shouldn't have done that. I heard that locals stopped that guy from putting a plate on the hotpool side of the creek too. I would suggest you just bring rope, set up whatever system you think of to cross, then take you gear with you when you leave.