Despite these clear material impacts on the lives of migrants, millions of people globally continue to cross borders without authorization—meaning walls are relatively ineffective. The first reason is that on longer borders, it is extremely difficult to fence the entire length and adequately guard it. Building fencing or a wall also entails acquiring the necessary land, building and maintaining roads, and supplying the necessary manpower to guard the barrier. The U.S.-Mexico border only has fencing over one-third of its 1,969-mile length