In and around the southern diamond-mining region of Sperrgebiet, certain roads are completely restricted or access controlled. There’s a checkpoint along the Orange River near Sendelingsdrif where you’ll be asked for your vehicle papers and Namibian Road Fund Administration permit. Don’t lose this permit, which you’ll have received from your rental company, or when entering at the border. You’ll be asked to produce it whenever you’re stopped by officials.
Otherwise be aware that Namibia’s roads can be dangerous, and many accidents often involve only one vehicle. The gravel roads are often so straight, wide and empty that it’s tempting to drive too fast. Sudden dips, turns and changes to the road surface catch out many drivers. Stray animals are also an issue and for this reason in particular you should never drive at night.