Among the best at establishing properties (7)
I believe the answer is:
estates
'properties' is the definition.
(estate is a kind of property)
'among the best at establishing' is the wordplay.
'among' says the answer is hidden in the clue.
'ESTATES' is hidden in the letters of 'best at establishing'.
(Other definitions for estates that I've seen before include "The dead leave them" , "lands for development" , "residential areas" , "Country properties" , "Extensive landed properties" .)