You can Lightning Flash up onto the cliffs in Sand if there isn't a sandstorm going on. The cliffs are actually dense, so no projectiles can fly into or through there (AOEs work fine).
This wasn't much of an issue before, but now it is, because people who will not be named are using it to afk train while being mostly safe, out of sight, and unable to be reached without the requisite 26 speed. People that melee them cause them to turn around to swing (this is especially for str and nin trainers) so people with low health pools can't just take the opportunity to pick them off.