Vehicle going over hard territory down under? (4)
I believe the answer is:
bush
'territory down under?' is the definition.
(the bush is an area in Australia)
'vehicle going over hard' is the wordplay.
'vehicle' becomes 'bus' (I've seen this before).
'going over' means one lot of letters go next to another.
'hard' becomes 'h'.
'bus'+'h'='BUSH'
(Other definitions for bush that I've seen before include "Shrub; axle lining" , "Remote country" , "ex-president" , "Outback" , "Bull is often associated with this" .)