Soapy water never worked for me... Pour kids bubbles into a bowl and use a paint brush to spread the bubbles on the top ring. If there is a hole you'll see it begin to blow a bubble where the hole is. patch with vinyl repair kit.
I would wager anything you slide into the ring would need to be air tight. Without the air it would not have buoyancy, Without buoyancy, when the ring gets pushed down, when entering or exiting the pool, the water would overtake the ring.
Salt - spread over pool - sweep in Acid - mix in bucket (adding Acid to water!!) then spread over top of pool Bi-Carb - mix in bucket then spread over top of pool Pool Clarifier - mix in bucket then spread over top of pool.
For amounts - ask your pool guy (or go to pool shop for free testing and they will tell you amounts)
Well there are two solutions.
1st: fill the pool with water. (yes it will be leaking)
Get a small bowl and put some dish soap in it.
Next tape a sponge or a rag (or something you can apply the soap with) and scrub down the sides with the soap. Because the soap reacts with water and releases oxygen (or Co2, I'm not sure) when it does, it will bubble up and reveal where the leak is.
I think that's the most reliable way. Another way is only reliable if the leak is large. You can make everyone get out of the pool and listen very carefully at each side. If the leak is large enough you'll hear a sizzling.
I think that the first method would be more efficient, but the second sounds like it might do the job as well and would be easier.
To fix the hole, I believe that you'll have to fix it with a patch kit. The link below lists a few different options. It's essential to have a patch kit when you have a vinyl above ground pool because it's incredibly easy to get a hole in the side. I'd suggest buying a quality patch kit to insure that the patch lasts. You don't wanna waste the 120+ dollars on annoying recurring holes in the side.
Put some Ivory dish soap, about a tablespoon, in a quart bottle with a sprayer, and fill the ring with air.
Then start spraying the soap solution all over that ring. When you see "Bubbles" appearing, that is where the leak is. Patch it. Fill with air & repeat. If no more bubbles, you have fixed it.