The fence is on a slope but it's minor. The theory is all lines that are exactly parallel must converge to the same point. Slopes just alter the altitude of the horizon line where the differences connect (think 2 or three horizon lines) so parts of the fence has different vanishing points vertically.
Find the parallel lines, the stairs for instance, or the part of the fence that isn't sloped, and trace from there. Should end up just left of your avatar roughly