I had an issue with a previous mare not wanting to cross a wooden bridge (funny that she would walk right on across the way high bridge over the noisy interstate but not the little bitty wooden bridge over the dry (at the time) stream bed.) It wasn't the typical trail obstacle bridge, but a regular wooden bridge about 20' long that cars drive over, so most of the wood is covered by soil/gravel.
At any rate, I would ride her up to the bridge, and she would slide to a stop without putting one foot on the bridge. I would urge her forward, and she would spin around and try to head for the house.
I decided that day that we were going to cross the bridge or else. I had hubby ride his horse on down the road and wait for us about 200 yards away. Mare tried spinning around about a half dozen times. I finally held on to the reins and the saddle horn in one hand (never claimed I could ride very well, and I am SUCH a chicken!) and smacked her rump with the riding crop with the other hand. Not hard, but pretty smartly. Mare was pretty shocked, and jumped forward. She tried to spin around again on the bridge, but I faced her forward and threatened another smack with the riding crop, and she walked right on.
Coming home, she didn't even hesitate. Guess she just needed to be outstubborned?
At any rate - sometimes it helps if you just keep your horse facing forward and not let them get away with refusing. If they even take one step toward the obstacle that "scares" them, it's a victory on your part. Let the horse think about things after that one step, then ask for another step. You will get there, it just takes time and patience. It also helps to have a trail buddy patiently waiting on the other side!
Plain Old Dee, horses Dancer and Rain I believe in dragons, unicorns, good men and other mythical creatures!