While this isn't always the case, puncturing the outer housing is most often caused by folding the cable or winding it too tight and small. If the cable gets a hard kink or a fold in it, the wire can escape the housing. Since you had this issue twice, and we rarely get reports of this, without seeing it this is my best guess as to what happened. You can always send a photo and we can diagnose better. If it was a manufacturing defect and you're under warranty we'll take care of it.
I admit that I'm not easy on headphone cables as I tend to walk around while wearing headphones. However, the DUM cables have not lasted as long as many other cables I've owned. I think the issue is that the inner wire is too stiff and the outer fabric's weave is not tight enough.
I've had the best luck with lightweight flexible cables like the ones from Impact Audio (which sadly seems to have closed). Audeze cables used to have a lot of problems and then they switched to a similar design and the problems are gone.
I'd be happy to send you photos, if it would be helpful. The cables are no longer under warranty. If they were, I would have contacted you, since I've always found your support to be excellent.