Keeping Iron Cross under cover (6)
I believe the answer is:
roofed
'under cover' is the definition.
(thesaurus)
'keeping iron cross' is the wordplay.
'keeping' indicates putting letters inside.
'iron' becomes 'fe' ('Fe' can be a synonym of 'iron').
'cross' becomes 'rood' (term for a crucifix).
'fe' put into 'rood' is 'ROOFED'.
(Other definitions for roofed that I've seen before include "(Of house) covered" , "shelter" .)