Guards daughter, beginning to expose criminal property dealers (8)
I believe the answer is:
defences
'guards' is the definition.
(a defence is a guard against something)
'daughter beginning to expose criminal property dealers' is the wordplay.
'daughter' becomes 'd' (genealogical abbreviation).
'beginning to' indicates taking the first letters.
'criminal property dealers' becomes 'fences' (a fence is a receiver of stolen goods).
The first letter of 'expose' is 'e'.
'd'+'e'+'fences'='DEFENCES'
(Other definitions for defences that I've seen before include "legal cases for those charged" , "Protections or justifications" , "Means of protection" , "barricades" , "ramparts?" .)