Hot Tub Concrete Base Query

[rdwessex]

Hi. A little advice please...
I want to build a concrete base for my hot tub. The base will be about 2.5 m in diameter. I'm thinking about 6" deep, set in the lawn. What's the best way to make the circle that'll hold the concrete? Some plastic or metal strip or something I can make into a circle, fix into the ground, pour the concrete in, then remove once all the concrete is set.
Thanks.

 

[kingandy2nd]

Probably a plastic soffit board will do, as long as you put plenty of wooden steaks behind it for support.

 

[jj4091]

Or this, that I use for edging lawns an borders https://www.google.com/search?q=100...NC4yuAeSBMIHBTAuMi41yAcW&sclient=gws-wiz-serp