Cracking the tough nuts who CANNOT get their cadence up

Those of you that know my mechanics methodology will recall that I insist that an increased cadence should not be sought as a primary objective, but should rather be a result of the forward lean & the unloaded downward application of force, until the foot hits the surface. Thereafter loading takes place as momentum causes the pelvis to continue forward, but the foot is grounded & the psoas, hip & soleus, & associated tendons & ligaments load elastically. While this is still completely correct in my estimation – I have the hardest time teaching athletes to fire the glutes & not the psoas concentrically. Today I had something of a breakthrough – while working with an older marathon runner (not the lady in the pic - she is a pro IM athlete!) for about the 6th or 7th session, who has a very slow stride rate: Despite doing the intermittent application of resistance across the pelvis from the rear with a harness which, as usual, increased his power application correctly, as soon as I backed off, he again engaged the psoas & started lifting again.
So I went against my better judgment & ran next to him & told him to match my cadence no matter what – i.e. move up stride rate as a primary objective. He popped upright, lost power, but looked great & the level of dissipation (& consequent reduced impact sound) decreased dramatically & all I had to do was have him reinstitute the lean & voila he was a racing machine!
Conclusion: Metronomes work as cadence guides, as long as the forward lean aspect is addressed & upward oscillation is limited/eradicated.