I don't mean to derail the conversation, but I just noticed today that one of the sites I work with (aptcorner.com) has dropped off of the first page of results

I don't mean to derail the conversation, but I just noticed today that one of the sites I work with (aptcorner.com) has dropped off of the first page of results for the company name (it was previously at around position 4–5. Is it not enough that I've set the preferred domain in webmaster tools? Will setting a rel=canonical tag make a difference?