Behind back, one put in charge to make counter-attack (9) = RETALIATE
behind = TAIL, back = reverse, ??
Historic bridle path decaying terrace joined (6,3) = ROTTEN ROW
decaying = ROTTEN, terrace = ROW
Rotten Row (a corruption of Route du Roi) in Hyde Park originally formed part of King William III’s carriage drive from Whitehall to Kensington Palace.
Positioned in a river, an Australian river (8) = ADELAIDE
positioned = LAID, a = A, river = DEE