If you want to make a sturdy roofless boar pen, you can half sink palisade walls into the ground with beams.

Place 2m beam vertical on the ground, then snap a 45 degree beam to the top of the vertical beam. Then, aim under the 45 degree beam to get the palisade wall to ''sink'' into the ground, creating a shorter outer wall for the pen. I usually line the inner wall with roundpole fence parts, with a single small wooden door with a thatch 26 degree roof over the top of it to protect from rain damage.

You can also cultivate the centre to grow turnips, onions or carrots at the save yourself time & space if needed.

https://steamcommunity.com/sharedfiles/filedetails/?id=2914657938