Formal/Academic:
* The line of demarcation between the two countries was established in the treaty of 1872.
* Philosophers have long debated the line of demarcation between science and metaphysics.
* The researcher carefully drew a line of demarcation between the control group and the experimental group.
Figurative/Informal:
* There's a clear line of demarcation between what I consider acceptable behavior and what I find offensive.
* The new manager drew a line of demarcation in the sand, outlining her expectations for the team.
* I've tried to be clear about the line of demarcation in my expectations for this project.
Remember, the best way to use "line of demarcation" depends on the context of your sentence and the message you want to convey.