New trenches, concrete blocks, sandbags and numerous checkpoints appear to be everywhere around Ukraine’s second city of Kharkiv, which has pushed back one Russian assault and is preparing to defend against another. A pink stuffed toy marks the entrance to one freshly dug trench in the regional capital. The cut earth is still soft and black and the soldiers are down to their vests, soaking up the sun. Tensions have eased in this northeastern corner of Ukraine, but Kharkiv, just 30 miles (50 kilometres) from the Russian border, remains under permanent threat, and a second line of defence has be…