If the runnaway civ is on another continent, consider building a strong navy and harrasing their coastal cities (pillaging fishing boats, attacking their navy, and killing any wayward embarked units). Most of the time they will respond by building a navy piecemeal and attacking you with one unit at a time, which is entirely counterproductive, particularly if you're using privateers. You don't need to actually conquer any cities. A strong navy can harrass indefinetely, break access to food, break trade routes, and cause the AI to waste hammers throughout the remainder of the game or until you're able to muster the forces for a land assault.