Here the 1858 Wright edition accidentally changed the plural strong holds to the singular strong hold. This reading was followed by the first two RLDS editions. The 1908 RLDS edition restored the correct plural (though not the original two-word spelling). The singular strong hold was undoubtedly a typo since the plural in the immediately preceding verse was left unchanged:
The change to the singular in the second verse thus contradicts the plural reading in the preceding verse. (For the spelling strong hold—that is, as two words—see the discussion under Alma 50:6.)
Summary: Maintain the plural strong holds for both occurrences of the noun phrase in Alma 58:1–2.