Complex sentence: Police checkpoints were established in all entrances of red-light districts during the hours of rehearsing or practising music where the names of the visitors in red-light areas were recorded in police register frightening the clients away.
Split into simpler sentences: Police checkpoints were established in all entrances of red-light districts during the hours of rehearsing or practising music. The names of the visitors in red-light areas were recorded in police register which scared the clients away.