Apprehend thug at ground where the gullible may venture? (2,3,6,4)
I believe the answer is:
up the garden path
'where the gullible may venture?' is the definition.
(as in leading someone up the garden path)
'apprehend thug at ground' is the wordplay.
'ground' indicates an anagram ('grind' the letters into a new form).
'apprehend'+'thug'+'at'='apprehendthugat'
'apprehendthugat' with letters rearranged gives 'UP THE GARDEN PATH'.
(Other definitions for up the garden path that I've seen before include "to the stocks?" , "Where one may be mistakenly led" , "the wrong way" .)