I find that they strenthen up all by themselves after a while. One thing I'd say though is, dont grow them too long. You dont need to with an electric anyway. When I was doing classical for a while I kept breaking them on things as you need them long for that picking technique but with the electric, you only have to just catch the string. I find that the thumb just needs to be that bit longer, which is a naturally strong nail anyway.
I practice picking with the thumb once on each string then a double pick on each string then three, then four, then the same with all the other fingers(including the pinky) before I even think about playing anything. And I also pluck the string slightly harder than normal playing.
It really helps me get the feel of the length of my nails on the strings as I keep them as short as possible to keep them strong and loud.
Anyway thats my tuppence worth on the matter and I'm still crap at it anyway but the nails are just fine
