After much consideration, and thank you everyone, for the input on footing in my prior post, I have decided that footing is as much about moisture as it is about materials.
I am planning a sprinkler system for my outdoor arena, which is about 210 x 150.
I am editing the original post because I had originally thought I could use “gun” type impact sprinklers set back from my arena fence. But my fence is too close to the retaining wall to do that, so I am now planning on pop-up type sprinklers mounted to the arena fence. I want a good timer system so I can cycle them.
Would GREATLY appreciate any advice and tips.