Historical clue formulations

• Guarded — 2026-02-13
• Obtain — 2025-12-13
• Password-protected, say — 2023-06-05
• Fix in place — 2020-12-09
• Like passwords, one hopes — 2020-09-07
• Impervious to hackers — 2018-03-14
• Encrypted, perhaps — 2011-05-14
• Nail down — 2008-05-28
• Safe — 2007-07-22
• Land — 2007-04-08
• Batten down — 2004-03-10
• Bolt down — 1994-03-04