I mean was there a DMZ or something or an mutually accepted line that both sides agreed on did it hit a river or lake or mountain and that was that? I'm assuming the Swiss stationed large numbers of troops there.
The River Largue used to mark the boundary between France, German Alsace, and Switzerland. Basically the French occupied one side of the river and the Germans the other, and didn't really mess with each other too much. The Swiss had several watchtowers and various buildings to monitor any action and ensure it did not spill over into the Swiss border. However, the fighting was not heavy south of Verdun, and thus there was little action besides watching each other. World War I is strange in how normal life was in some areas, and how warring it was in others.
It did not look like the coast in Northern France, where barbed wire literally ran out to the beach. It was much less fortified and inhabited.
Why didn't they launch large offensives near the Swiss Border where the opposition was less fortified? As both sides were clearly trying to break the stalemate for years, wouldn't have this been an easier option?