another good idea
make back /flip that stops you, but
when you do /f your car is repaired instantly, but gets flipped after random time varing from 3 to 5 seconds
so if you do /f just at the edge of cliff, you won't be able to abuse it as instant brake
also random time (from 3 to 5 seconds) will make you not able to predict when to do /f to use it as brake