strongbad is wrong
if you nair in place and fox tries to run at you and sh nair, he cant beat it
this still isnt amazing or anything, because he can full jump nair, up smash your foot, and probably lots of other dumb stuff
but im pretty sure that unless youre moving towards him, he cant go through your foot when youre nairing
and yeah, if youre dash dancing, just dd grab or retreating stomp/bair, but you gotta mix in nairs when he starts planning the overshoot to make up for your dd and he runs into your only move with decent priority