|Looking down from the top the fact that the insulator is compromised is not the least bit obvious.|
Touching the post gave quite a tingle when the fence pulsed. That may be one way to find these situations. Put the multimeter on "hold" and tape one end to a metal walking stick and probe the posts.
The other way would be to train the dogs to home-in on the ticking sound, although I don't think Herc will be too enthusiastic anytime soon.