I like the idea but could be a bit expensive. What else would you use for larger and more permanent jobs?
1.) Grommets and bungee cords are ridiculously cheap.
2.) It's 38" x 80" banner. That's nothing. 21sq.ft. of banner material -- on a fence? The fence is taking basically all the wind load, not the banner. If you have wind loads strong enough to damage the banner in any noticeable way, you have much bigger issues at hand (e.g. is this property located inside a jet engine wind test tunnel?)
3.) Having issues with stainless steel tie wraps? (#1, stop using sh*t chinese fasteners, #2, stop cranking them down like a snare drum, #3, purchase a quality 1,000-1,200 denier banner, with a proper hem, designed to last more than a weekend)
4.) Banners are not permanent signs - not by any metric. If you want something "more permanent" and aesthetically appealing, use the proper materials and fasteners ($$$). But if you're stuck on a "permanent banner" (lol), there's a zillion "fence fasteners" out there: