well i want to make a section where theres fog or (cloaked units) im afraid they'll wander away so whats the most effient way to dectect them out side a loaction

Stop. Think for a second. Edit your post using proper grammar, use punctuation so we know where your question is. Use parts of the title in the actual body of the post, so we know what's going on. Go read the rules.

If XXX brings exactly 0 units (or at most xxx units) to location you want them to stay in. That's the easier way to detect it.

well thanks 0.o