Long piece of metal placed on shelves at guardhouse (8)
I believe the answer is:
barracks
'shelves at guardhouse' is the definition.
Although both the answer and definition are verbs in their -s form, I can't see how they can define each other.
'long piece of metal placed' is the wordplay.
I cannot quite see how this works, but
'piece' could be 'r' (abbreviation for Rook) and 'r' is found within the answer.
'metal' could be 'ra' (Ra is an example) and 'ra' is located in the answer.
The remaining letters 'backs' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'on' acts as a link.
Can you help me to learn more?
(Other definitions for barracks that I've seen before include "Cheers ironically" , "Military encampment" , "Buildings for soldiers" , "Accommodation for soldiers - jeers" , "Large block" .)