Well, if you want Shinies you can always use chaining methods (PokeRadar and consecutive fishing) where the chances can be increased to 1/200, but if you really want to find Shinies via hordes:
Use a strong move like Surf or Heat Wave, to faint all targets when there are no shinies in the horde. (Or just run away from it, of course) Though when you do find a shiny after your long shiny hunt then use False Swipe on the shiny, and another random move on the other four, so it can be the only one on the field and you can catch it.
The reason there are not many horde shiny hunting guides is because chaining is so much easier. Like I said, it will be a 1/200 chance of getting a shiny via chaining. So, I'd recommend chaining over encountering hordes.
Hope I helped. :)