Anyone who knows me knows that we eliminated most flexion exercises from our workouts years ago based on the work of Dr Stuart McGill. This is one of the most difficult things for coaches and trainers to hear and, to get them to implement. In the last few years we have popularized the terms anti-rotation and and anti-extension and taken these concepts from physical therapy to the gym floor. Here is a great mainstream article about Dr McGill that will help you reinforce this with your clients.
This will really help you sell a program of planks, anti-rotation exercises and rollouts to your clients.
Michael Boyle's Strengthcoach.com Blog 