When Trương Như Cương (張如岡), a pro-French collaborator, coerced his colleagues to sign a petition to the Thành Thái Emperor to promote him to the position of viceroy (副王, Phó vương), Cao Xuân Dục refused to sign - instead he wrote a quick poem on the petition.
A relief of Cao Xuân Dục was sculptured on a wall in a cave in this local region to commemorate his righteousness.[3]
Cao Xuân Dục retired in 1913 to concentrate on building his library, Long Cương Bảo Tàng Thư Viện (named after his pseudonym), collecting and maintaining Vietnamese literature.
Cao Xuân Dục made significant contribution in maintaining Vietnamese culture and literature in 19th and 20th century.[5] He spent many years writing, collecting, copying, re-writing and preserving valuable books including:
^Bradley Camp Davis, States of banditry: The Nguyen government, bandit rule, and the culture of power in the post-Taiping China-Vietnam borderlands University of Washington 2008 - Page 104 "Cao Xuân Dục"
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