Carrying the bike in the back of the car

[Pedal Wench]

Yup - bikes are upright, and once clamped by the fork, won't/can't tip over, unless the board with the fork mounts is tiny - one that goes across the lenght of the back is impossible to tip.

So, does this mean the bike is upright? If so, how do you keep it from falling over? I can see how the fork mount keeps the front of the bike from tipping, but what about the rear?