They are here to ensure no one crosses the barriers.
Soldiers are guarding a barrier
Just because someone is ensuring that no one crosses a barrier does not mean they are soldiers or that the barrier is being guarded.
exists p1 s1 x1 x4.(n_barrier(x4) & n_thing(x1) & Topic(s1,p1) & Actor(s1,x1) & a_here(s1) & -exists e1 e2 x2 x3.(Theme(e2,x2) & Actor(e2,x1) & v_ensure(e2) & Theme(e1,x4) & Actor(e1,x3) & v_cross(e1) & (x2 = x3) & n_one(x2)))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_guard(e1) & n_barrier(x2) & n_soldier(x1))