Wear down some huge rodents (5)
I believe the answer is:
erode
'wear down' is the definition.
(to erode is to wear down or decay)
'some huge rodents' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'ERODE' can be found hidden inside 'huge rodents'.
(Other definitions for erode that I've seen before include "Wear away with weather" , "fragment" , "go to pieces!" , "Corrode" , "Gradually wear away" .)