My only suggestion is that you kinda suck some of the air out of him/get him tired doing circles at a trot or easy lope before you try running. Is he cowhorse bred by chance? My brother had a Mr. San Peppy mare that he got when she was 7 or 8 and until the day we stopped riding her, she would crow hop at the oddest times and none of us could ever get her broke from it, it was just her personality. I hope my suggestion helps some, good luck!!
And welcome to the forum by the way.