Come back concerning aggressive dog (5)
I believe the answer is:
recur
'come back' is the definition.
(I know that recur is a type of come back)
'concerning aggressive dog' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'aggressive dog' becomes 'cur' (I've seen this before).
're'+'cur'='RECUR'
(Other definitions for recur that I've seen before include "Persist" , "Perseverate" , "expected to return" , "Happen again (5)" , "come back to one's mind" .)