An option I hadn't originally mentioned would be to trench the length of the post holes and add a drain. Trenching the length of the fenceline would have been a lot of work and likely destroyed a handful of productive fruit trees.
After conversing with my neighbor it turns out he has a drain pipe 6 inches (15 cm) into his property line used for his rain ...
An old claim staking trick is to first dig the hole to the depth you want. Put the post (claim corner) in the hole. Pack 1 inch (large) gravel only in the hole. Wiggle the post to pack the gravel around the post. The pebbles wedge between each other, the post, and the side of the hole. Work the gravel into the hole until the post stops wiggling.
Works as ...
I have heavy clay that won’t drain. I dipped the end of my pressure treated posts in liquid asphalt (roofing material) and let them dry before cementing them in. 20 years, and they are still in pretty good shape.
Your other option is to fit a short concrete post, and bolt the wooden post to it. It's more expensive, but the concrete won't rot when the hole fills with water.
Around here they're often called a 'grandfather' but apparently the official name is a 'repair spur'
Dig them deeper, perhaps 6ft or even 8 and fill up to level with the pea gravel.
That should provide sufficient volume to drain the water from the posts. However there may be other water seeping in.
One solution I saw was to drill into the post from the bottom and meet that centre hole with a small hole from one face. The bottom hole is capped and then a ...
What if you poor the concrete into the hole before inserting the post? Just wiggle it down? Seems like that would be easier than trying to poor concrete around the pole.
Curious to know the outcome of your project
You are looking at a swaged cable end, specifically a threaded tensioning type of end. Special tools are needed to perform the swaging, especially if the part is stainless. I've used hand swaging tools for aircraft cable, but the fittings are far more malleable than stainless.
But you're in luck, as my searches found swageless cable components specifically ...