Slip Leashes are a great light training tool that are excellent at teaching leash pressure, and are impossible to slip out of if fitted properly! They're great for escape risk dogs, or a quick leash to throw on when needed during off-leash adventures. They come with a stopper to keep the leash snug at the base of the neck to prevent the loop becoming too big.
I always use slip leashes with foster dogs, who usually know how to slip their collars if wearing a flat collar and regular leash!