I don't agree that the "only person it benefits is you". In a fence out state, it would seem that the benefit would accrue to the one who does not want cattle grazing on their land. While it appears Hippie rancher has no intention of allowing his cattle to graze on neighboring land, it would likely be ruled in his favor, should that occur. For that reason, it would be best for the foundation to pay for the fence, in order to prevent that occurrence. Personally, I would at least ask for a financial contribution, and point out the local land laws. If turned down, I would end up paying for it myself, because I don't want animals out of my control, even if that is within my rights.
We have a similar situation here. We have a mile of fence bordering one of Knife Rivers rock pits. The fence is in very poor condition, and would not keep animals in. We abandoned that pasture a number of years ago because it is mostly wooded and the terrain makes fencing very difficult. With the drought now extending for about a decade, I had hoped to repair the fence in order to graze some of the high meadows. We approached local Knife River management about sharing the costs. State law requires that both sides pay for fencing, whether or not they both graze that land. Knife River indicated they would not share expenses. We did not pursue it, because it would likely cost more in legal expenses than what we might have eventually received. I had actually hoped that they would volunteer some equipment hours to clear the line. I suggested it, and they did agree to have someone survey the line, which I was good with. It turned out the "surveyor" was just a guy with an Onx app on his phone. He marked things well inside our border which he admitted. He said he was told to just assure we didn't cross over onto their line. The pit had tried to buy some of the hillside from us in the past. Their current operation breaks some DOGAMI rules regarding the steepness of the slope along our border, so they could be required to fill in or purchase land from us to correct this. If I wanted to be confrontational, I might have pointed this out. Our access is through Knife River land, so I really don't want to get into a situation where they make things difficult. We have always had a pretty good relationship with the pit. At least that was always true before it was sold to Knife River.