Rearing Horse

["G & J Thom" <thomlabs@netbistro.com>]

Hi everyone,

This is not entirely endurance related tho the horse we
are having trouble with was to possibly be started in
endurance rides this year.  My friend has a 5 yr old 
arab mare .  This mare goes very well under saddle in
the arena and around the yard.  As soon as we head away
from home always in the company of another horse, we
get a certain distance out never the same spot and this mare
will all of a sudden start rearing and striking with her back legs
and will refuse to go on.  Even when you get off and continue
to walk her in the direction you want to go she will rear for a
few steps.  My friend and I are not horse trainers and were 
wondering if 1)  If this is something we should tackle ourselves
                  2)  If a trainer fixes the problem is it something that
                       may start up again later.
This horse has lots of potential for endurance and we were taken quite
by surprise when the mare started this.  This mare is bottom of
the pecking order in the herd and has never really indicated that
she had a temper like this.

Any advice will be greatly appreciated.

Julia