There was a deleted verb N. gartho “defend, keep” in The Etymologies of the 1930s based on the root ᴹ√GARAT, an extension of ᴹ√GAR “keep, maintain, defend” (EtyAC/GAR).
Neo-Sindarin: I think it is worth restoring ᴺS. gartha- “to defend” for purposes of Neo-Sindarin, but for “keep” I would use better known S. heb-.
Conceptual Development: This verb had other meanings in Tolkien’s earlier writings. In the Gnomish Lexicon of the 1910s it was G. gartha- “admire, have affection or respect for” based on the early root ᴱ√gṛþ- (GL/42). The Early Noldorin Dictionary of the 1920s had ᴱN. gartha- “to set, put in position, appoint” (PE13/161), perhaps related to the early root ᴱ√ƷARA “spread, wide places” given the noun ᴱN. garth “place” from the same page in this document.
A name appearing in The Etymologies from the 1930s with the gloss “Fenced Fort”, a combination of garth “fort” and thoren “fenced” (Ety/ƷAR|GARAT). It may be a variant of Arthoren “Fenced Realm”.