I can make a wall in an arc but not oval.
If there is a way, please let me know.

You probably tried it with two halves of a circle. Your're correct that doesn't create an oval.
You need a wall split in 4: wide curve, sharp curve, wide curve, sharp curve. You can play with the lenghts and curve degrees to get a smooth oval. For other randomly curved walls: for every change of curvature use a extra (part of the) wall. It's an easy way to create random curves for a small natural pool or lake, or the sides of a river.


A trick for a full circle: create one wall and curve it 180°. Copy&paste, then rotate the copy 180°.