Two obstacles, very large: it’s for a Russian invasion (10)
I believe the answer is:
barbarossa
'a russian invasion' is the definition.
(Operation Barbarossa - German invasion of Russia)
'two obstacles very large it's' is the wordplay.
'two obstacles' means two replacements for 'obstacle'.
'obstacle' becomes 'bar' (I've seen this before).
'obstacle' becomes 'bar' (I've seen this before).
'very large' becomes 'os' (abbreviation for oversize).
'it' becomes 'sa' (old-fashioned abbreviation for sex appeal).
'bar'+'bar'+'os'+'sa'='BARBAROSSA'
'for' is the link.
(Other definitions for barbarossa that I've seen before include "emperor" , "Frederick I" .)