Always use a good chain, to anchor your bike to a light pole.
Had a friend who chained his bike up outside a pub, using a 20000Lb tie down chain (from a Hercules aircraft) and a big brass lockwood lock. When he came out, he found that some one had tried to steal his bike. Evidence, 1/2 dozen broken hacksaw blades and a wrecked lock. After all that effort, the Bastards chose to take the chain instead of the bike....