Station some detectives outside the post office (5)
I believe the answer is:
depot
'station' is the definition.
(I know that depot is a type of station)
'detectives outside the post office' is the wordplay.
'detectives' becomes 'det' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'outside' means one lot of letters goes inside another (some letters go outside others).
'the post office' becomes 'po' (abbreviation).
'det' going around 'po' is 'DEPOT'.
'some' acts as a link.
Can you help me to learn more?
(Other definitions for depot that I've seen before include "Headquarters - storehouse" , "Storage location" , "Storehouse, repository" , "Storehouse or warehouse" , "Store for large quantities" .)