Frequent spooking

The best approach to spooking, according to trainers, is to redirect your horse's attention by changing his focus. "Horses are linear thinkers so that normally they can only think about one thing at a time," Scoggins says. "If you can get your horse's mind on doing something else, he will be less inclined to react to whatever has him spooked."

There are tons of material out there on how to desensitize your horse to different items. I use Clinton Anderson's methods.  Desensitize at home - get the horse used to plastic bags, tarps, jugs with coins rattling in them, pool noodles, etc.  If it moves, makes a noise or both - use it.  Do this at home and by the time you get back on the trails you will find the response much better.  Just make sure your timing is right and you are rewarding the right thing.

I'm looking forward to trainer101's ideas on this, too.
How can you make the behavior more difficult than being good.  When she starts that mess, work the snot out of her somehow.  Real hard, real quick then act as if nothing happened and go about your ride.  Next episode, repeat the quick hard work.... then release and ride calmly.  That's just a guess.  I really don't like to be one horses that spook.  I guess if I was in my Australian saddle I'd feel more secure than in my English saddle.

Thank you for the ideas.  I appreciate your thoughtful comments and I will keep on.  I guess I just needed to hear it from somebody else.

A lot of miles seems to be the answer with most of our horses, plus establishing trust so that even if something is scary, they trust you to not take them somewhere dangerous.  Our paint used to be solely an arena horse and at first the trails were a big, scary place with horse-eating boulders, killer squirrels, ghostly flying grocery sacks, evil construction tarps and such.  He's so relaxed now.  I think age might have something to do with it too.  My Cody was fearless when he was younger and I led him everywhere.  Now he's 6 and a little less sure of things when I'm up on him.  He will go past scary things but does a little dart to escape once he's past!  Our POA who is 17 is pretty much bombproof unless you happen to be a mariachi band or the other day some kids came flying down our road on their bikes around some bushes up behind him. 
 
When Cody does spook, we start practicing flexing, doing serpentines, turns on the haunches, forehand so he has to think about me instead of whatever it is he's not sure of.  Goodluck AND wear your helmet!!!!!