Actually fox is the only character for whom you can't get out consisntently with just ASDI up or even an SDI input up. You're more likely to just get bad DI on the launcher hit for your troubles. Even if you don't try to smash DI out and instead DI away for the laucher, it's still a tech chase set-up, with ROB being able to cover 3/4 options with another dsmash. This is part of the reason I feel ROB actually goes 6:4 against fox.
A perfect shine OoS will hit frame 4 as fox after shield stun, which is also the same frame ROB can act after a boost->fair on shield, meaning it would probably hit them. however, a perfect shine OoS is a ground shine OoS, very difficult to pull off consistently, and if you miss it you will also not hit ROB if he dashes away or glide tosses away after the boost fair, and you commit yourself to a double jump which ROB can punish even if he dashes away with a boost->uair.
I would recommend actually trying to CC the boost fair at low percents. It'll lead into a shine which can lead into waveshine combos which are super easy on ROB, and you can put him at a low angle offstage with it which is where his recovery isn't very good because he doesn't have a good ledge sweetspot with his up-b, enabling you to shine gimp him. At mid to high percents you won't be able to CC boost fair, so you'll either be forced to DD around it's range, trying to bait it out for a punish, or try to out prioritize it with nairs. Alternatively if he jumps too high try to get underneath him where he can't threaten you with a boost.
EDIT: also no dandizzle, optimal ASDI/SDI for dsmash is straight up.