I don't mean to be in the least bit facetious, but there are two entirely reliable methods of ensuring correct spelling. Jack Tarlin has touched on one - a thorough check and critical reading of your literary efforts; the other is a good dictionary.

The best of spell checking programs will let you down in the end - ask any English teacher. Don't trust 'em - they ain't your friend, and they are happy to make you look like a public idiot, which is the very finest kind, of course.

Cheers,

PKH