Get more response to your 'leg' at home where you are not in danger. If you want to be able to ride a horse past 'new' scary things out on the road or trail, you have to have 100% control at home.
The 'leg yielding' exercises I use will get an obedient horse past just about everything. If it doesn't, you just do not have enough obedience instilled into your horse. The key in teaching this to a 'boogery' horse is to 'set him up' at home. I like the safety of a big pen or an arena to teach this. You just have to set up things you know he will not want to go past AFTER you have him willingly 'leg yielding' without obstacles.
Like everything else 'new', I want to do this schooling on a horse that is settled and quiet. I think it is a HUGE help to do this after a long ride and not with a 'fresh' horse.
NOTE: Do not 'show' any of these things to your horse before you attempt to ride him past them.
If he does not like garbage cans, set one up in a pen without showing it to him. I would set it right next to the fence or rail. I would ride past it repeatedly, turning him toward it right after he passed it and riding him past it again while it is on the other side of him. I would do this over and over -- for 2 hours if necessary -- until he just walks by with his head turned slightly away for the object and your inside leg holding him over very close to it as you go by.
Then, I would set it out about 20 feet away from the fence or rail and ride him between it and the rail. I would gradually bring it closer and closer to the rail until I could 'push' him right through when it was only 4 or 5 feet from the rail.
Next, I would throw a tarp over the fence and ride him by that -- same routine. When he would do that, I would drape the tarp over a barrel (or that dreaded trash can).
When I was working with horses and riders working toward CLEET certification, we used shopping carts, brightly colored barrels, people in big rain coats, and even used a pen with a pig in it and one with ducks and geese in it.