The contributor says her husband says this when she doesn’t feel like cooking for dinner. The malaphor prompts a visual of the family opening the refrigerator and fighting for the best leftovers. This is a mashup of “stand on one’s (own) two feet” (act independently) and “fend for (oneself)” (take care of oneself without the assistance of others). I suppose the speaker was thinking of the word “fend” but uttered “defend” instead. A tip of the hat to Lori Snider for sending this one in!