Characters that want to stay out of sniper-sights have to develop a personality and get a Rep. Players must be too cool, too evil, too important, or even too weany to shoot. They must be interesting. The least interesting, uncool-nobody is the first to get shot. That's just another lacky. That player is soon after shot.
Opponents have no respect for faceless nobodys.
Even the Terminator will go down if shot by a sniper with a big enough gun. Attitude is the only defense left to the players. No one shot them in the back, even if they had shotgun ready and aimed. Attitude even won the duel for Holliday vs Ringo. Snake got a chance to fight in the ring and escape.