DANDONG: Rifles slung over their olive green uniforms, the North Korean border guards watch warily as the Chinese speedboat surges towards them across the Yalu river. The boatman ignores them, drawing his craft within half a dozen metres of the bank and then, turning parallel, reduces speed so his passengers can photograph the dismal promenade of rusting hulks, motionless cranes and shoddy buildings on the outskirts of Sinuju, North Korea