Cliff tile in the way

is there a such trigger that forces a unit to stop right where it is when a cliff set is in the way?
if you ever played a td, you'd notice they try some other way around

I think it is a region-related trigger.

This trigger is for terrain cliffs.

Event:
A unit enters region (insert region name here)

Conditions:
((triggering unit) is a hero)) equal to false
((Owner of (Triggering unit)) equal to (insert player here)

Actions:
Order (triggering unit) to stop.

That is region related. If you are refering to them coming within a certain distance from the cliff, i think it can be done by doing this:

Event: a unit comes within (insert range # here) of (insert point here) (i am not sure if there is such a event option. i don't have the enitor in front of me.

Conditions:
((triggering unit) is a hero)) equal to false
((Owner of (Triggering unit)) equal to (insert player here)

Actions:
Order (triggering unit) to stop.

I think those 2 triggers will help you. I wold double-check that second trigger. It may contain false trigger fields.

Basically you have to map out all of your mountains with regions because there is no event that can trigger by simply running into terrain since terrain and triggers are independant except for running through them of course ^_^ as far as the program is concerned.