My stock tensioner broke so I'm giving this a try. The roller is from Tractor Supply and has been discussed on this forum but mounted on the seat post.
I'm using it bolted down, but it could also be configured to swing loose and attach to a spring.
Once I'm satisfied with the position, I will anchor the bracket to the chain stay with a self tapping screw to prevent rotation into the spokes.
(Looking at the photo while previewing this message, I think I might try facing it the other way, toward the back wheel, to get the bolt heads away from the chain)