Leave them alone. If I get killed by a sniper it's for one of three reasons: 1) a skilful sniper shoots me and I die. I have nothing to complain about. 2) I walk round a corner, see the lens flare of someone hardscoping, it's too late and I'm dead. Tough luck. Corners exist, the other guy set a trap and I walked right in. 3) I walk round the same corner again, looking for revenge. Same result. And again. And again. It isn't down to the sniper or the sniper rifle that I'm stupid and can't look for another way round or another enemy to fight.