Allow service members to save their leave as they desire. Do not take away any excess leave based on their decision to not take any during that Fiscal year. Instead do not offer to buy it back but allow them to save it unconditionally and apply it toward their departure or retirement of the military.
So if a military member is about to retire and their 20 year mark is identified, they have 142 days of leave saved up, they should be able to retire full out right 142 days early from their 20 year mark by turining in their unused leave days. This would cut down on service members being paid in full for days they were on leave and also keep them at work rather than taking leave knowing they are saving up for an earlier retirement.