Oracle - Necesito ayuda para crear dos Triggers (1 before, 2 After)

create or replace trigger modificador

   before update of manager_id on departments

      DECLARE

      v_emp employees.employee_id%TYPE;

   begin

      if(

        select count(employee_id) INTO v_emp from employees where employee_id=80);

      end if;

      if :new.department_id=80 then

        RAISE_APPLICATION_ERROR(-23344,'No puede modificar el manager id al agregar un empleado del departamento 80');

      end if;

end;

Error que empieza en la línea: 2 del comando :

create or replace trigger modificador

   before update of manager_id on departments

   begin

      if :new.department_id=80 then

        RAISE_APPLICATION_ERROR(-23344,'No puede modificar el manager id al agregar un empleado del departamento 80');

      end if;

end;

Informe de error -

ORA-04082: referencias NEW u OLD no permitidas en disparadores a nivel de tabla

04082. 00000 -  "NEW or OLD references not allowed in table level triggers"

*Cause:    The trigger is accessing "new" or "old" values in a table trigger.

*Action:   Remove any new or old references.

TRIGGER MODIFICADOR compilado

Errors: check compiler log

CREATE OR REPLACE TRIGGER acsel.cheque_01

 AFTER

  UPDATE

 ON acsel.cheque_emp

/*REFERENCING NEW AS NEW OLD AS OLD

 FOR EACH ROW*/

DECLARE

BEGIN