Pigeons are messy and cause disease!
Pigeons having once decided to set up a house at your home, will continue to stay there until they are made to move. Even after decided to make it difficult for them, they might continue to try to stay. I have seen them work around spikes (metal and plastic), I have seen them work into chicken wire by using their head to inch their way pass the obstacle. It is important to check the work after installing whatever method is used.