Bungee cords: some above have scorned the idea, but in the right place they can be an asset.
We used to make pole banners for local towns. There's a big light pole with 2 two-foot long arms coming off 14 feet up, 5 or 6 feet vertically apart, and a plate welded on the end.
A 2 ft x 5 or 6 ft vertical pole banner with a pocket/socket/tube (call it what you wish, a wide hollow hem or seam) is slipped over the top arm, and over the bottom arm.
Because of the way the arms have the end plate, you need slack to get the banners on.
Once 'installed,' they flop back and forth, hinging on the top one, and stressing the bottom one in breezes, until the bottom one disintegrates, or the joining seam gives out.
Putting an eyelet above the bottom, and a bungee strap like used on pickup tonneau covers, tightens the banner, and removes the impact from the changing breezes action on the whole thing. The Bungee gives gently, and resists the 'attack'.
The top is a solid fix, the bungee just removes the overall slop and allows some play in the bottom edge.
It works for us.