I would also say the pinch collar. But do not pull back on it. Allow the Lab to pinch itself. Only release it when you are satisfied with the hold.

This can cause problems as well. At least with my spaniel. She would do the same. But the biggest problem was, after the pinch collar. She would squat in the rears like she wanted to sit. It took a lot of work to get the point acrossed to her but it was worth it.