Straps that never slip would be a wonder...but there is a device sold that is a strap that goes across your shoulderblades to hold them in place. I saw it and wondered, why in the whatever did I never think of that?
The modern day back cross-strapping (and the newer sports bras "V" strap) work pretty good, but elegant, these are not.
Thanks to you, I just looked, found this site: The Straps "Crossbar" I'd had no idea.
After my stunt with hook/eye injury to the spine, I got creative and began moving my bra straps (sewing) closer to the hook base of the bra, so the straps were CLOSER together. That worked fine. And it still works. But not with all bras.
The problem, as I discovered those many years ago; is that this "strapping" concept is really unattractive when wearing an opaque or fine-fabric blouse or dress. Looking at the photo at this site? I'd add a lacy "patch" in the middle of the bar-strap. Something with a texture, embossed, delicate, so it resembled a "fabric tattoo" under the blouse/dress.
Thanks, KAC, for inspiring me to look.
I think I've just found my next "wardrobe" enhancement project. :)