How do you stop trailer fishtailing?

To stop trailer fishtailing, first, reduce your speed gradually without sudden braking, as this can worsen the sway. You should also ensure that your trailer is properly loaded, with the weight distributed evenly and the hitch adjusted to the correct height. Additionally, using a weight distribution hitch or sway control system can help stabilize the trailer. Finally, maintain a safe distance from other vehicles and avoid sharp turns to minimize the risk of fishtailing.