u/HelloHyde

First spring in this house, and realized I had no idea where my sprinkler water shutoff was. After a ton of digging to trace the supply line, I finally found it under the grass with no cap or cover (second pic shows the grass plug I pulled out).

What's the best way to cover this so it's easy to access in the future? Put a round box around it? Looks like it had a yellow cap of some kind at one point, but it's long gone/broken.