One in charge having dog roll over (7)
I believe the answer is:
curator
'one in charge' is the definition.
(curator can mean a custodian)
'dog roll over' is the wordplay.
'dog' becomes 'cur' (both can mean a despicable person).
'roll' becomes 'rota' (rota is a kind of roll).
'over' says the letters should be written in reverse.
'rota' written backwards gives 'ator'.
'cur'+'ator'='CURATOR'
'having' is the link.
(Other definitions for curator that I've seen before include "Artistic director" , "Person in charge of a museum" , "Museum's administrative head" , "Keeper of a collection" , "museum boss" .)