You can usually find copper pipes already bent into nearly a circle at the hardware store. My idea would be to use one of them since you can then use premade fittings to attach a hose.
Instead of making a perfect ring out of copper, you could always make a nearly closed ring with one side attached to the hose and the other side just blocked off. I think that’d be easier.
Then drill holes for bubbles into the copper ring tube.
Or maybe see if there’s like a giant airstone they use for aquariums.
I think you’d definitely want to use some type of elastic-y epoxy to keep the ring in place. I think people would naturally kick it and prod it with their feet without realizing they’re doing it.
Yeah, I was going to recommend like a pond air ring diffuser, but you’d definitely feel like a fish in a bait bucket. Maybe you could make your own with fewer holes since there’s a lot of DIY YouTube guides on how to make those.
The idea is pretty simple since it’s just a hose fitted to a barb tee connector