My "arena" is actually just an open area of flat land where our roping arena used to be. It is grassy and just regular sandy dirt for footing (that is what our dirt is like anyway).
This is from standing nearly in the center to the south side looking east
And this is the same location looking west
I have always like the pipe panel fencing. That way, it's sturdy but still portable. Just put a good wooden post every little bit and it's good to go. If you decide you need to move to another farm/ranch/house/state/etc, then you can just take the panels down and take them with you, you can make the arena smaller/bigger as you need, or you can change the location of the arena on your property if you decide you don't like where it's at. One day, we plan to re-fence our arena area and this is the type of fencing we are going to get.
When they built our roping arena 30+ years ago, they used those welded wire "bull panels" for the fencing (it can be seen in the background here
) and after that experience, let me tell you, those things are dangerous
. If you have a horse bump into one a little too hard or even through just regular wear and tear, the welds will break and you end up with a mass of heavy gauge wire sticking out in every direction just waiting to impale any animal that gets close enough. Thankfully, the last of that fencing was torn down in recent years so we don't have to worry about that anymore.