I built a cave with many deep pitfalls. Then I put down the path grid as I have done numerous times on other mods.

But this time the Zombies are running after me (they are in combat with me) and falling into the pits.
I tried this with normal vanilla creature ands the same thing happens so it must be the floor they are on?
The floor is made of many large (20 feet wide) static rocks.

I am afraid that actors walking on static objects (unlike normal floors) like my rocks do not fear the edge and will allow the NPC to fall?

I did not think this was the case at first because I did the same thing with an archer up 100 feet on top of a rock as a sniper (the giant rock had 3 blue path grid points in a triangle on top of the rock ) and it seem to work fine as she did not fall off.

If this is the case (just lucky with the archer?) how do I keep them from going too close to the edge of these rocks and falling down in the pits?
I cannot use a collision box as this would prevent the player form falling as well.

There must be a NORMAL way to do this that is intended to work with out some "hacky" trick right?

Any suggestions?

Have you tried unticking the 'allow falls' on the AI package? I'm pretty sure that subspaces are used to make sure that NPC's don't use nodes they shouldn't.

I was thinking you could place subspaces over the voids but the http://cs.elderscrolls.com/constwiki/index.php/SubSpace says: 'In combat, an actor that is close to his target will move in a straight line toward his target, ignoring path grids and subspace boundaries.' so not much use.

ok, here is the scoop:

After 7 hours of trial and error scripting I finaly found the answer. The path grid must be EVERYWHERE that the player can possibly be at. IF you do this then the actors will NOT fall (more or less) trying to get to you even in combat.