Blind spots

I've been working away on The White Gallows for the past week, trying to tighten and clean the text. Every time I read through it I spot more small typos and quirky phrasing. My particular blind spot are small words - a, as, in, to, etc - which when I read the text are there, but in reality aren't, and hononyms. One reviewer picked up I'd used 'rye' instead of 'wry' in The Rule Book and I discovered yesterday that I'd managed to do the same in this one as well. It's very frustrating trying to spot a hole in the text when you're convinced that it's not there! I'm sure everyone must have some kind of blind spot ... I just wish I could cure mine. Where is an independent proof reader when you need one?