Shorts in electric fences: If you do this long enough you will see a bit of everything.

Looking up at the insulator you can see where there is a wrap of old wire around it. Knowing the history of this fence, it was probably soft wire that had been stretched by animals going through it and the fence repair crew "tightened" the fence by putting wraps around the body of the insulator.  Then, the next time the animals went through the fence they garroted the insulator.

Looking down from the top the fact that the insulator is compromised is not the least bit obvious.

I found two by listening but may have more of them out there.

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.