How can I set navigation limits on animated objects?

I am trying to find a way to limit the movement of 2 objects into a specific area that is small compared to the rest of my terrain. I am setting this area up as a trigger to "run" if anything hits the trigger but not finding a way to contain the normal AI "Idle, walk, eat" to stay in this trigger area. I have searched and found many saying navmesh but have not seen how to set navmesh for such a small area instead of the entire terrain. Is anyone able to point me in a direction that may help me configure something that will accomplish this? You can see the trigger box in the screenshot below and I would like to use that same box as a containment area. Any help is very much appreciated!