What should you do to stop a trailer skid effectively?

To effectively stop a trailer skid, releasing the service brakes instead of using them is the correct approach. When a trailer begins to skid, applying the brakes can cause the wheels to lock up, which can exacerbate the skid rather than help regain control. By releasing the service brakes, the wheels can start to rotate freely again, allowing for better control and stabilization of the trailer. This action helps regain traction by allowing the tires to make contact with the road surface without the added force of braking, which can lead to a better chance of steering the vehicle back on course.

In terms of other strategies, counter-steering can be helpful in some situations, but it needs to be executed with the understanding that over-correction can lead to further instability. Accelerating slightly would typically be counterproductive, as it increases speed during a skid, making it harder to regain control. Using the trailer's hard brakes would lock the wheels, hindering the ability to steer and regain control. Thus, releasing the service brakes is the most effective action to take to stop a trailer skid.