How to secure edges

I just put edging in all around it to hold the sand in. looks great. I kept the edging just below the edge of the pavers. hardly noticeable.

There are any number of ways but I find the easiest and most cost effective is to surround with treated lumber. It doesn't have to be anything big, maybe a 2 x 4 and some landscape spikes on the outside to ancher the lumber. There is also manufactured plastic edging but this stuff can be a pain. It pulls and it wants to spread or move and I find it doesn't weather very well in my area . If you bury some treated on the 2 side about half way and anchor it on the outside, your project will stay intact and level for a very long time.