Have never posted here before but figured you Hunt folks might be able to help me out. Big 18 Hand gelding, supposed to be draft and Selle Francias cross. He is a really nice horse good manners etc. but must have been trained with spurs because he is very responsive, (almost too much) to the leg and even gets a bit nervous. OK, biggest problem is his strength. He is very strong and has taken off with the rider - 30 year old man in good shape etc. We have tried many bits on him, Pessoa, Waterford, now in Double Jointed (mouth) Hackamore Bit. This seems to work right now, but he does seem to figure out how to evade the bits after about 3 weeks. Any ideas for a big horse like this?
Training.
(Training +) Gag.
You don’t say if you have checked the horse’s mouth? If he is otherwise well mannered, it could be pain, particularly as he does OK for 3 weeks or so before he tanks off again. Otherwise - training.
My 2 cents worth would be…get a gag.
However, I’d also want to know why he took off with the rider. Since you say he’s a really nice horse with good manners, what was being done with him that would turn him to flight like that? If the underlying problem is how he is being ridden, or what he’s being asked to do (or what Willesdon said about pain), then no bit in the world is going to be your sole answer.
If you feel spurs or rough riding are the cause of his tendency to be strong, then training is your issue. Horses can be sensitized or desensitized to leg.
Pain is totally different. A harsher bit that causes more pain can cause a horse to run harder.
Also look to saddle fit.
Pain
Please consider the pain aspect. Check for lyme and early epm as well as an over all thorough physical. Saddle fit may show up with loins and withers.
If you can have an osteopathy practictioner work on him, you may find a whole new calm and kind horse inside this one. I’ve had enormous positive changes in my herd from osteo.
Please feel free to p.m. me for more info.
Have you tried a running martingale? I always add that first before I “up” the bit. Sometimes that’s enough. If the horse pulls you might also try a Kineton noseband. That sometimes helps.
Have you tried a Pelham or a Kimerwicke? Some horses respond well to curb chain.
I hunt in either a Kimberwicke or a Waterford, depending on my preference that day. neither bit backs my horse off the bit too much, but both bits get his attention.
I prefer to mostly ride on a loose rein in the hunt field. Is
What does he do when he gets strong? Neck up and locked jaw? Head down and rooting?
In company or even by himself?
Out side arena only?
I find that lots of bending to unlock the jaw can help and what really helps is for the horse to get tired and still have to go, day after day.
Had one friend who switched to a bitless bridle and that helped everything. I’ve seen horses go well in the Mikmar contraption, then get used to it and the bit became ineffective. I once had a horse who always got used to strong bits and we never did get it sorted out, but I suspect looking back on it that I was clutching at him and not training enough. Oh well, twenty five years ago.
Really, the kind of bit depends on what he’s doing, and take a hard look at his energy level whether that means tiring him out or reducing rich feed.
Go rent a Myler combination bit. Works wonders. Lots of horses object to single joint bits or bits that work off the tongue. Combo bits put pressure on the poll and nose and give the horse the opp to respond before you even get into their mouth.
Try a port. This will free up the tongue and give your horse more freedom in the mouth so he can relax.
Of course, training but if you suspect he hates the bits you have been using you are probably right.
Do you think the horse may be putting his tongue over the bit? I had one who was soooooo strong and nothing worked except getting a rubber bit port (you add it onto the middle of any bit - it makes a very very high port they literally cannot get their tongue over.)
With it, he was hunter trials championship excellent.
Without it, he was … .alarming. : )
O.P. where are you?
The O.P. hasn’t responded at all to our questions.
I checked past thread quieries by the o.p. and that’s the pattern.
O.P. you need to participate, please…
Don’t ya just love it when you go to the trouble of offering “requested” advice the the OP just blows away???
A bit of knowledge is the strongest of all…
Flame suit on
Assuming this is not a pain issue, I’d put a few rides on the horse in a Mikmar training bit - http://www.mikmar.com/bit-pages/training-bit.html
I have one, and I love it. Mine is currently on loan to my mother to use while trail riding her 23 yr old paso fino bratty pony 
I love it because there’s no fighting the rider in this bit; they only fight themselves. I used it on my jumper for a while, and eventually moved him to a rubber gag, then a kk-ultra loose-ring.
I’ve used it on a number of horses and ponies as a ‘tune-up’ bit with great success. I have found that once the horse learns that it can’t pull and/or bolt, they are much better/more responsive and respectful of another bit afterwards.
Good luck!
Since we are just talking amongst ourselves, I have found that with some horses, esp. those with thin jaws (TB’s) respond negatively to harsh bits - the pain seems to make them just run off.
He might be a big horse, but they cannot be out-toughed.
Every time I’ve had a horse who seemed to need more bit, I went to a fat rubber straight bar snaffle and worked on softening and gaining trust. There is always a REASON for a horse running through a bit - fear, pain, lack of training, something. But going the harsher route is usually not a solid, long term answer, as you’re finding out. You need to address the cause, not the effect.
I agree with you Tiffani B!!!
