Indestructibility of a neck hair on neck regularly ignored, note (10)
I believe the answer is:
permanence
'indestructibility' is the definition.
(I've seen this before)
'a neck hair on neck regularly ignored note' is the wordplay.
'a' becomes 'per' (eg 'one a day' means 'one per day').
'neck hair' becomes 'mane' (I've seen this in another clue).
'on' means one lot of letters go next to another.
'regularly ignored' indicates alternate letters (letters removed at regular intervals).
'note' becomes 'e' (musical note).
The alternate letters of 'neck' are 'nc'.
'per'+'mane'+'nc'+'e'='PERMANENCE'
'of' acts as a link.
(Other definitions for permanence that I've seen before include "Lasting quality" , "stability" , "Continuity, durability" , "Indestructibility" , "Indefinite existence" .)