Have you tried turning around or changing direction? There is a harness called mekuti which can help with this

I was going to start a thread with the same question!! My staffie Coco pulls like a train and she too gets sore around the armpits. I've made her a temporary fleece to put under it (made out of an old fleece of Ethans!!).
I'd be interested to know how good this harness your hubby has bought as Coco has terrible skin and chaffes so easily.