Stella is the expert in this field.
During day I always use my hands for koura but another way is to place a net just down stream and disturb all the rocks etc and often the koura just flick backwards into the net.
Or chase them round the rocks with a net 8) works good too.
OR, get a piece of meat and tie it onto the end of a string and when the crayfish comes out of hiding they clamp down and u can pull them right onto land! usually I use this method for deeper water where I can't quite get in.