Theft regularly involving farm tool yonks ago (8)

'tool yonks ago' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'theft regularly involving farm' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'involving' means one lot of letters goes inside another.
'farm' becomes 'ranch' (ranch is a kind of farm**).
The alternate letters of 'theft' are 'tet'.
'tet' going around 'ranch' is 'TRANCHET'.