Hi Will. I too used to have good strong nails. They always say (who they?) that the hardest thing about being a guitarist is being born with the right kind of nails. I was, but about 20 years ago started having problems with nails becoming weak and brittle. I tried false ones, but found that they seemed to be designed for cats rather than men. Out of a packet of assorted sizes, there were none wide enough for my thumb - and I haven't got particularly large hands - and the smallest ones were more like talons. The ones I did manage to use were sort of OK, but the curvature was deeper than my nails, and after a while, they would go 'ping' in mid-song. Ditched that idea. Then I tried coating them with superglue, but that wasn't entirely successful. Then I tried supergluing strips of cotton cut from an old shirt across the ends of the nails, and it works. You need a couple of coats of superglue, and when it's hard, use an emery board to smooth it out. It usually lasts   for two or three weeks, but that rather depends how much exposure to water it gets. Not too sure whether it's doing any damage, but I've been doing it for several years, and my nails haven't fallen out. One of my problems is that I get ridges running the length of the nails, and they split along the ridges. It's a bloody nuisance, even if you don't need the nails to pluck with. (By the way, I too have tried finger picks, but can't get used to them. I think you need to have used them from the outset, or they just don't feel right. I've heard other nail- pickers saying the same thing). One time when I was at the doctor's, I mentioned it to him. He said "Oh yes; I get that as well". Which was a great help. I read somewhere several years ago that this was caused by zinc deficiency. So I bought a bottle of 100 zinc pills, and religiously took one a day for the duration. Didn't make a scrap of difference. I recently read that ir was caused by iron deficiency, and am currently working my way through a bottle of iron pills, but so far haven't noticed any difference.
John Kelly.