When deploying a roof ladder from another ladder, what should always be used?

Using a leg lock when deploying a roof ladder from another ladder is essential for safety and stability. The leg lock technique involves positioning your leg against the ladder to secure it in place while you are reaching for and deploying the roof ladder. This technique helps ensure that your weight is distributed properly and provides a solid anchor point for body control. It minimizes the risk of slipping or losing balance while performing the task, which is crucial in a firefighting context where safety is paramount.

The other options, while they may have their own applications in ladder safety and stability, do not directly pertain to the specific action of securing yourself and the ladder when deploying a roof ladder from another ladder. A belt harness might be used for different scenarios of securing personnel, and a stabilizing strap or a ground anchor plays a role in securing ladders in general but are not specific to the action of deploying a roof ladder. Therefore, the leg lock technique serves as the most effective and appropriate choice in this context.