(Suggestion: if adopted, this one should be titled something like "Limitations on Leaves of Absence")
LIMITATIONS ON LEAVES OF ABSENCE
With the exception of leaves of absence for military duty, no leave of absence, by itself or in combination with other periods of leave, may last longer than six months. Any employee who for any reason or combination of reasons misses a total of six months of work in a twelve-month period, or a total of nine months of work in an eighteen-month period, will be separated from employment due to unavailability for work. Any employee so separated will be eligible for rehire and will be able to apply for any vacancies that may exist at any given time, depending upon qualifications and availability of job openings.