The phrase "a decade he maintained" is correct and usable in written English.
It can be used to describe a period of ten years during which someone upheld or continued a certain condition, belief, or practice.
Example: "For a decade he maintained his commitment to environmental conservation, inspiring many in his community."
Alternatives: "for ten years he upheld" or "over a decade he sustained".
For 3 decades, he maintained a private practice in Infectious Disease, HIV, and Travel Medicine and was Hospital Epidemiologist at Sequoia Hospital where he also served as President of the Medical Staff for 2 years.
Ketchum began taking ten milligrams of Dexedrine, first intermittently, then three times a day — a habit that he maintained for decades — and he studied in bouts, memorizing swaths of information.
For more than a decade, Armstrong maintained his innocence by insisting that no drug tests ever revealed that he had doped.
The comments about unwanted sexual advances and groping women did not matter because they were more than a decade old, Trump claimed, yet he maintained that former President Bill Clinton's indiscretions and scandals ― and his wife's response to them ― were fair game.
Over the decades he also maintained a peripatetic freelance career, appearing often in free-improvisation settings with leading European and American artists, including poet Yusef Komunyakaa, pianists Aki Takase and Irene Schweizer, drummer Famoudou Don Moye, saxophonist Oliver Lake, singer-guitarist John Lennon, Cecil Taylor's Orchestra of Two Continents, and the Instant Composers Pool.
During the first two decades of his academic career, he maintained a traditional view of sexuality and "hardly knew a soul who was not heterosexual".
He has overseen a decade of maintaining the status quo and an annus horribilis for the leadership – complete with lurid tales of Ferrari crashes, family fortunes and even murder.
After nearly three decades awaiting execution for a crime he maintains he did not commit, Mr. Rivera was faced with a life-or-death choice: he could get a chance to leave prison, but only if he relinquished his claims of wrongful conviction.
For two decades he consistently maintained that the Israeli-Palestinian conflict could only be settled on the basis of mutual recognition.
She added that the shelters were sturdier than the "lower-quality shelters built by other organizations" and could last up to a decade "if well maintained".
