Impossible to track without perfume (9)
I believe the answer is:
scentless
'without perfume' is the definition.
('perfume' can be 'scent' (synonyms) so maybe 'without perfume' can be ''scentless')
'impossible to track' is the wordplay.
'impossible' becomes 'less' (I am not sure about this - if you are sure you should believe this answer much more).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'track' becomes 'scent' (both can mean a trace left by someone).
'less' after 'scent' is 'SCENTLESS'.
Can you help me to learn more?
(Other definitions for scentless that I've seen before include "Not providing bouquet" , "Having no smell" .)