Sponsor rebuilt great pond (9)
I believe the answer is:
godparent
'sponsor' is the definition.
(godparent is a kind of sponsor)
'rebuilt great pond' is the wordplay.
'rebuilt' is an anagram indicator.
'great'+'pond'='greatpond'
'greatpond' with letters rearranged gives 'GODPARENT'.
(Other definitions for godparent that I've seen before include "as one responsible for charge" , "Baptism sponsor" , "Religious guardian" , "Pet dragon (anag)" .)