Sally Hanson (could be Hansen?) do a clear varnish that strengthens them to stop them splitting. It really does work too. You can get it in any chemist or supermarket.
hiya! I had this problem some years ago. My nan told me of a remedy that I was sure wouldn't work. Chivers Jelly cubes - just eat one a day. apparently it's the gelatine that does the trick. You know the ones - the square blocks of jelly that you dissolve in boiling water. They are divided up into smaller squares and you just eat one of these a day. Believe it or not it does work.So NOT JUST AN OLD WIVES' TALE!!!!!!