Cactus very much requiring intervention of a protector? Not entirely (7)
I believe the answer is:
saguaro
'cactus' is the definition.
(saguaro is a kind of cactus)
'very much requiring intervention of a protector? not entirely' is the wordplay.
'very much' becomes 'so'.
'requiring intervention of' indicates putting letters inside.
'protector?' becomes 'guard' (guard is a kind of protector).
'not entirely' means to remove the last letter.
'a'+'guard'='aguard'
'aguard' with its final letter taken off is 'aguar'.
'so' going around 'aguar' is 'SAGUARO'.
(Other definitions for saguaro that I've seen before include "Giant type of cactus" , "Large branching cactus" , "Huge cactus" , "Branched cactus" .)