It shall be unlawful to discharge any firearm, bow and arrow or air gun in the Village or so that the bullet, arrow, missile or projectile therefrom enters the Village without written permission from the Mayor, provided that this Section shall not be construed to prohibit any officer of the law to discharge a firearm in the performance of his duty; nor to prevent any citizen from discharging a firearm when lawfully defending his person or property; nor to prevent the discharge of bow and arrow by students upon school grounds while under the direct and immediate supervision of teachers or other school supervisory personnel.