Not so much a 'Fall-Back' but a useful sticky-footer pattern with good browser support.
HTML:
<body>
<div class="sticky-footer-wrap">
...
<footer class="sticky-footer">
...
</footer>
</div>
</body>
If you need the .sticky-footer-wrap container be a nested more deeply, it's parent/wrapper elements should include the class .sticky-footer-outer-wrap unlesss the those wrappers already have height: 100%; CSS applied:
HTML:
<body>
<div class="sticky-footer-outer-wrap">
<div class="sticky-footer-wrap">
...
<footer class="sticky-footer">
...
</footer>
</div>
</div>
</body>