Hi – I have an Irish Draft and went through something similar when I first bought him and he had been a field hunter. A clinician I worked with pointed out that the reason my horse would walk or trot a few steps than slam on the brakes and refuse to move (there was no physical explanation, I had him checked nose to tail including xrays of feet etc etc, blood tests) was that he didn’t respect me. The clinician, Don Sachey, suggested I look into Clinton Anderson’s approach to natural horsemanship and groundwork to gain respect without threats and well without brute force. I got the dvds, I audited a 3 day Method clinic and diligently worked with my horse with success – he does backslide occasionally and I now do the groundwork a few times during the week to remind him that this is not a democracy. It’s important to be safe, to keep yourself safe and your horse safe. Instead of relying on your whip to move your horse forward, consider investing $20 in a pair of ‘dressage’ spurs, they have blunt “teeth” on the side of the spur and as with any spur or aid, less is more -it’s another tool to have when you need it but don’t abuse it or your horse. Good luck with your cob.