Soldier guarding back of unit alongside tense, tough instructor (8)
I believe the answer is:
martinet
'tough instructor' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'soldier guarding back of unit alongside tense' is the wordplay.
'soldier' becomes 'marine' (I've seen this in other clues).
'guarding' is an insertion indicator.
'back of' says to take the final letters.
'alongside' is a charade indicator (letters next to each other).
'tense' becomes 't' (abbreviation used in many dictionaries).
The final letter of 'unit' is 't'.
'marine' placed around 't' is 'martine'.
'martine'+'t'='MARTINET'
Can you help me to learn more?
(Other definitions for martinet that I've seen before include "Rigorous figure" , "'Disciplinarian, exacts strict conformity to rules (8)'" , "Despot" , "Trite man becomes a tyrant" , "Strict disciplinarian - met train (anag)" .)