Proof...

that a horse amd a fencepost can not occupy the same space at once. I watched two geldings get frisky, bucking and running and playing in the high winds...then watched the small one come to a perfect sliding stop inches from the fence. He was followed quickly by the large one, who solidly cross-checked this 5x5 and created yet more fence work for my old self. No brakes, i guess.

They do it here too,every so often, one will try an slide into home base, unintentionally of course, after too much stall time due to inclement weather.
You want to let em out, but sometimes the pasture is too slick. It's a different ball game from now til spring, as to when they can go into the pasture or just the riding arena, they sure need their "out" time and all the rest, can keep a person real busy they can.

What I do not like about the southern yellow pine they pressure treat and mill for posts, smaller dimension like 4"-5" is given that its one of or the only needle bearing species, that is or almost is a hardwood (correct me here), and they are brittle. That knot is a tell tale sign, just drop one like that from about 12'-0" up, it will snap in half and leave a point, luckily the point was on the top half that broke off. Those darn post and rail fences do it to, we have a fair amount of that, and they snap near a pocket and leave a sharp, dangerous point sticking up, we have had good pulling these, gluing and clamping, not to be cheap, they are expensive so I do repair any that will glue up, they are pressure treated, but not S.Y.P., seem like a hardwood though.

It sure is fun to watch them play, but no fun to repair fences.

Since I started using electric fences, I have no maintenance due to horses. They don"t get close.

All my maintenance has been from trees or limbs falling on the fence.

Had an oak go down across the fence. Even with part of the fence on the ground, horses never got out.

My experience is like Nancy's.
When we had horses, the electric fence was the answer.
All they had to do was touch it once, and it seemed like they could smell the wire from then on, or maybe hear the harmonic in it.
Anyway, they would go near the elec. fence, but not through it.
However, no fence of any kind matters to a bull if he wants out.
I heard a story about elephants, Why can they stake out a grown elephant to a tent pin?
Because as a baby, he is staked out to a post he isn't strong enough to pull up, so he grows up thinking he can't pull the pin.

You know, that knot was probably the key! I took a good look at it again today and I think you're right!