Marine rover? (3,3)
I believe the answer is:
sea dog
'rover?' is the definition.
(thesaurus)
'marine' is the wordplay.
I cannot really see how this works, but
'marine' could be 'sea' (both can mean 'of the sea') and 'sea' is located in the answer.
The remaining letters 'dog' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for sea dog that I've seen before include "Old tar" , "Old or experienced sailor" , "An old sailor of canine origin" , "Dosage (anag)" , "Experienced mariner" .)