How about "post-graduate Marine"?
ONCE A MARINE, ALWAYS A MARINE:
Once a Marine, Always a Marine: This truism was adopted as the official motto of the Marine Corps League. The origin of the statement is credited to a gung-ho Marine Corps Master Sergeant, Paul Woyshner. During a barroom argument he shouted, “Once a Marine, always a Marine!” MSgt. Woyshner was right. Once the title “U.S. Marine” has been earned, it is retained. There are no ex-Marines or former-Marines. There are (1) active duty Marines, (2) retired Marines, (3) reserve Marines, and (4) Marine veterans. Nonetheless, once one has earned the title, he remains a Marine for life.
http://www.usmarinesbirthplace.com/United-States-Marines-facts.html