Animal rights protected by measures (6)
I believe the answer is:
ferret
'animal' is the definition.
(thesaurus)
'rights protected by measures' is the wordplay.
'rights' becomes 'rr'.
'protected by' is an insertion indicator.
'measures' becomes 'feet' (foot is a kind of measure**).
'rr' put within 'feet' is 'FERRET'.
(Other definitions for ferret that I've seen before include "It drives rabbits from their holes" , "Fierce little animal used in rabbit hunting" , "Jill perhaps" , "Rummage" , "Root around" .)