Finish before the rodents re-organise, prevalent (7)
I believe the answer is:
endemic
'prevalent' is the definition.
(I've seen this before)
'finish before the rodents re' is the wordplay.
'finish' becomes 'end' (synonyms).
'before' becomes 'e' (I've seen this in other clues).
'the rodents re' becomes 'mic' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'end'+'e'+'mic'='ENDEMIC'
'organise' is the link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for endemic that I've seen before include "constantly present in the locality" , "Widely prevalent" , "Commonly found in a particular country or people" , "Localised" , "Restricted to a certain area" .)