Ideally, this horse should not get to the point where he is over & on the
ground with you trying to hold him there! As I'm sure you already realise,
this horse is dangerous & may seriously hurt the rider or himself. This
being said (& probably easier said than done)...
First, what is he doing when he resists & rears? Is it a time when he is
resisting the bit, asked to go forward or backward, when approaching
particularly scary things? If this is a way to avoid situations he
dislikes, it needs to become less convenient to resist than to give in to
the rider's request. If this is a way to avoid bit pressure, it is time to
look at the bit used or the rider's use of hands and other aids.
One horse I aquired some years ago did similar rearing. (That's why he was
given away. His old owner was scared of him.) If he didn't want to cross a
ditch, leave the barn, etc., he'd rear. As an experienced & confident
rider, I was able to throw weight forward while pulling his head sharply to
one side. This resulted in him coming down onto all 4 feet and then cirling
until he was VERY tired of it. We then attempted to go on with our ride.
We repeated this each time he resited by rearing until it was no longer
worth his while to rear.
If you feel that your friend's horse may be resisting because of her use of
hands or because of the bit, change to a snaffle without shanks. (I am
assuming that you are <not> talking about a curb bit w/ chin srap & a broken
bar mouth piece - terminology differs in some parts of the country.) The
mildest bit possible is a large egg but snaffle or a straight bar snaffle.
Another option is to move to a bosal.
Has the horse been checked for saddle fit (rear because of pain) and had his
teeth checked by a dentist? This might be worth while as well.
Good luck. Send a little more info on what is happening when he rears.
Maybe I can offer more specific help.
Linda Flemmer
Blue Wolf Ranch