I did the fiberglass thing for a while, but over time, my "real" nails got really thin.
I read a suggestion to use hoof cream (Different than Hard as Hoof). I brush on a coat a couple of times a week. I think it actually makes my nails softer and therefore more flexible. I haven't broken a nail since I started using it.
https://www.chewy.com/mane-n-tail-ho...SABEgLRG_D_BwE