Long ropes would tend to cut sharp corners, for example where the canal suddenly widened after a bridge or at a junction between canals. Vertical rollers were sometimes erected to ease the passage of the rope. At other bridge holes this was not done, and the wet towrope, full of stone dust from the towpath, wore deep notches in the brickwork arch. Engineers built bridges with smooth parapets of rounded coping stones or bull-nosed bricks. Boats don't have brakes To slow down or stop, you cannot put a horse into reverse.
Wooden bollards are the answer.
The cotton tow-rope is given one or two loose turns around a bank side post and then pulled tight. Friction between the wood and rope can act to slow up to 30 tons weight of boat as it runs past, resulting in posts with sculpted waistlines, the remains of which can be seen all around the system.