Minimum fence height next to ravine
Check for any "attractive nuisance" laws as well. Even if not specifically present, you could face legal liability if a kid came into your yard, climbed the fence into the ravine, and got hurt. If that happened, having the opposing side able to state that you replaced the existing fence with a shorter one isn't going to look good.

Not a lawyer, but for fencing surrounding something potentially deadly like a ravine, I'd suggest fencing that's tall and not very climbable. Wrought iron or similar could work to create a impassible barrier while not disrupting sight lines.

EDIT: looks like this law probably won't apply, because attractive nuisances have to be artificial in nature. That being said, reducing the chance for a neighbor's kid to die horribly in your yard could be motivation enough.