[FILE - In this February 8, 2016 file photo, Macedonian Army soldiers erect a second fence on the border line with Greece, near the southern Macedonia's town of Gevgelija. Six nations from Central and Eastern Europe meet Monday in Prague to discuss plans for a new “line of defense” for Europe that involves a double fence along Greece’s northern border. (AP Photo/Boris Grdanoski, File)]WARSAW, Poland (AP) — So where should the next impenetrable razor-wire border fence in Europe be built?