In all three of these situations, a guide line or lifeline from the exit to the diver is the standard method of reducing the risk of being unable to find the way out. A lifeline fixed to the diver is more reliable as it is not easy to lose, and is often used when diving under ice, where the line is unlikely to snag and the distance is reasonably short, and can be tended by a person at the surface. Static guidelines are more suitable when a lifeline is likely to snag on the environment or on other divers in the group, and may be left "in situ" to be used for other dives, or recovered on the way out by winding back onto the reel. Guidelines may be very much longer than lifelines, and may be branched and marked. They are used as standard practice for cave diving and wreck penetration.