so the AI keeps use demilitarized zones on my cities to gain points, thats the first problem.

The other is how do you use demilitarized zones. i cant seem to find a button or option anywhere in the game to set one.

theres nothing on the net, forums, youtube, or even the tutorials that even talks about how to set them or use them.

Dmz is affinity of diplomatic culture, so you have to pick it up first. It will be in up right corner.

I don't own the expansion but I suppose that it works in a similar way of "Under one banner" (the ability peculiar to expansionistic cultures)

You now playing builder culture, so you have the builder affinity icon. So, if you pick up diplomatic culture, then instead of builder affinity you will get dmz button

In industrial era the diplo culture are Scots

got it, its only if you have the right culture,  took me a min to figure out what you ment. 

Thank you! it would have taken me forever to figure that out as none of the diplo cultures have intrested me and i never would have noticed till i used one.