S Narayan wrote:

Nothing, you are on a vector. You have to trust the controller that he (or
she) knows what he's doing and doesn't forget about you. It would be wise to
be situationally aware by using GPS or VOR radials (or other means) to tell
if you are likely to run into rocks.

TCAS, or even a Garmin 296, removes a lot of concern about rocks during
vectors. A moving map of the MVA would even be better and is being evaluated by
some high-end avionics vendors.