The building of additional protective infrastructure around a couch fort. Couch forts being predominantly made of pillow and potentially mattresses, thus sandbags would theoretically be made of apple pies. Popularised by the Melbourne Fort Builders Anonymous society.
Andrew: Gee Rach, you've gone to quite a bit of effort with sandbagging the moat of this week's fort
Rachel: You know it, these apple pie sandbags look silly now, but when the Saxons turn up, they ain't gettin anywhere near my Bulls jumper.