Also, it's been my experience that sometimes I don't want the back-link to go to the footnote number itself, but rather to the beginning of the paragraph that the footnote is in (or some other appropriate place). Otherwise, some readers will jump back with the footnote itself on the first line of the display. Putting the back-link a little earlier in the text preserves some context for the footnote.
And in that case you would need both <a anchors in the body of text, nacherly.