What to do if a horse continues to kick and stomp while trailering?

This is common with barrel horses it seems. My friend used kick chains with great success. Research them on Google and I've added a link below of them. They aren't harmful but stop the kicking and eventually break it altogether. You can also buy sideline hobbles that you put on them when they are already in the trailer. It allows some movement but no kicking. Also adding an unbreakable mirror and small salt lick or secure toy alleviates boredom.

The horse could be doing this for a number of reasons that make it unhappy in the trailer. If it is just impatient, and is okay loading, then just make sure that there is plenty of shock absorbent flooring and padding (rubber sheeting) behind it so that it can't jar its hooves if it kicks out.

If it is just anxious and unhappy, it could be hating being alone.. some horse owners report very good results after putting a mirror up - make sure it is a stable mirror (unbreakable). We found it was easier with a young horse if they travelled with a companion, so you could try this with a little pony that is happy just to go along for the ride, but make sure that the companion isn't a fat little pony whose feet might suffer just standing for long spells.ADDITION: have just been reading some of the answers given about hobbles, kicking chains, etc., and am appalled. If this is what goes on in the world of barrel racing, then thank god I have never come face to face with any of you who recommend. All my working life with horses covering 50 years I have tried to ensure that horses are encouraged to become willing partners, and have been blessed with some amazing equine friends. Nothing is achieved without time and patience and hopefully this way us humans will be granted an insight into the intelligence and heart and willingness that equines are born with. Shame on you.

I would strap a leather with buckle and 6" chain just above the knee,need to know which leg He is using;