The front of the intake is covered by a fine mesh - I believe the teechnical term is FOD guard (Foreign object damage)
All the Wrent turbines that I have used have come with this mesh built in.
However bumps on the road may lead to premature bearing wear due to the extra stresses.
Thrust reverser / deflector. Techinically I would make a deflector - like a rudder which can be operated by a servo. It would have to be a mild steel plate that can withstand EGT (exhaust) of over 800 'C.
At speed I would think you'll need deflectors of some sort but for the low throttle manouvors maybe split the brake system to left and right side of the car and mix it with the steering channel.
For slower speeds, four wheel steering would probably help out alot.
The thing I worry about with thrust vectoring or a traditional rudder is matching how those want to turn the car compared with how the wheels want to turn the car. With these systems I picture the rear of the car being pushed sideways instead of actually turning the car. To ensure better steering at higher speeds + thrust levels, I think a rudder mounted over the front axle would provide the best and most natural "feel".
There was a jet powered Baja 5b on a topgear DVD a little while back- topspeed around 90mph I believe whilst drag racing a Porsche. This is pretty sweet though, steering issues aside.