If I was the buyer, I'd rather have a brick/paver mowing strip terminating the lawn, rather than a strip of gravel. It's tidier, more durable and looks better. (The pool would be where the landscape bed is.)

Yardvaark, that was the idea, but I need to fill it with something. Ie the inside of the ring. We may be using retaining blocks set down some to act like pavers/bricks though to follow the grade as there is a step down to deal with to the flat area.

So you need a curb where the soil level changes.

The second pic in my post shows that there is a rise in the ground surrounding the pool and below I've highlighted the area that is a step down from existing grade which then levels out on the sides and becomes more flat just outside the view of the picture. The red line is where it is the tallest.

I wonder if something like this would work even though it is grass around it an not a paver patio. We may add a paver path to the edge from the concrete, but not sure how to do the edge and get it to stay level with the grass and be able to drive the lawn mover tires (lawn tractor) on it so it doesn't collapse too. Also what do you use inside the ring that can keep stuff from growing into the pool/liner and then when the pool is removed easy to add the material where the pool was.

The tallest height is 12" but it doesn't stay that for more than a few feet.