Barbas is my favorite follower, you can avoid being nudged off cliffs by staying a good distance away from them, avoiding them, or simply just keep moving so he doesn't get a chance to get near you. If Barbas gets hostile, use the 'Animal Alliegience' shout and he should calm down and no longer be an enemy. Who doesn't want an invincible dog for their travels? The only problem is, sometimes you can't take him in a few quest required places, so I'd suggest being able to conjure up allies!