Fences are a reasonably new phenomenon in Mongolia. Most of the country is unfenced and the herders live a nomadic lifestyle. Even near the Aimag Centres and the Soums and Bags there are no fences. However, this changes when you get into the Soums, Aimag Centres and such, with fences now enclosing parcels of land that Mongolians now own. The rest of the country is still unowned (I guess this means that the government owns it) and people and animals roam as they will.
The Soums and Aimag Centres are becoming more like everywhere else in the world now with property fenced.