Horses usually buck the first time out of fear. Once they have made it a 'habit', they just prove that "Horses are creatures of habit!". Now, he needs no reason if you have ruled out saddle fit and pain.
Longing one with a saddle on and letting them buck on a longe line just teaches many of them to buck better. Once a horse has made a habit of bucking, especially if the horse has bucked people off, ground work often times does little at all to help. They just get really good at groundwork while they ride like pigs or don't ride at all.
Is this horse broke to tie? If not, that is where I would start. I used to buy a lot of horses off of the track, both TBs and QHs. Teaching them to tie solidly was the first thing I did with every one of them.
Then, I would take a big, heavy stock saddle that fits well, that has a good mohair girth and has a good wool felt saddle pad. Use a pad with a 'cut-back' front if he has high withers. Then, let him stand saddled (with a breast collar) for several hours at a time for several days. Unsaddle him right where he stands and do not lead or longe him with a saddle until he accepts it completely. Start out with the girth fairly loose. Snug it up a little at a time after he has been stand for a while with it. He can either be 'fussy' about the saddle on his back or he can be 'cinchy'. I would tend to think he is cinchy or at least started out that way. The bucking got started and now he just does it because he does it. He will tend to keep getting better at it. He is now using it as his manifestation of 'resistance'.
Does he have a good or bad attitude about everything else? Is there a lot of resistance or bad-a** attitude over other things? Some horses are just obnoxious and have unwilling attitudes. Others have 'triggers' that you just have to let them work out but not let them practice their bad responses.
And by the way, he does not need time off. It is not a 'trust' issue. It is a 'respect' issue that revolves around accepting the saddle and then the rider after that is accomplished. Trust come from respect. You cannot coddle one into being respectful and obedient.
Last edited by Cherie; 10-04-2013 at 08:54 AM.