The Adobe Oven Base blocks movement, and is very easy to build. Therefore it is often used for sheep pens. It is efficient but ugly, and not really intended. The reason that it blocks movement is that it would look strange for people to “pass over” the oven base. However, doesn’t it look much stranger that you can keep sheep in a pen made of half-built ovens?
It is supposed to be a lot of work to get domestic sheep, so the oven base pens are an exploit to make things quicker than intended.
A long time ago, the Trash Pit was what people used to build pens. It was even more efficient than Oven Bases. However, the Trash Pit was changed so it now decays after a while, which made the Trash Pit pens disappear.
We could either make Oven Base not block movement, so it would not hold animals in, or we could make it decay to adobe or rubble after a few minutes, unless you build the full oven. Both would solve the issue of low-cost, ugly sheep pens. What do you think?