The idea of authorizing certain individuals on school property to have guns to protect students isn't new.  But a state senator wants to clarify exactly who is permitted to possess guns for that purpose.   Senator Mike Regan, Republican from Cumberland and York Counties, wants to expand the definition of a "school resource officer."  He wants to include under that umbrella county sheriffs and deputy sheriffs.   His legislation also sets standards for training, and allows schools to hire certified security guards from private companies.