Nice Arcadia revive.
Lesse, what would I try...
If he's Fairing right over the ground then he's got a nasty wall up for you. I think you might be able to literaly run right past him if you stay right outside his range and time it right though. This could follow up to the Bair, or something more sneaky like SideB to HA. I don't see this being practical, but it's worth the thought.
Other ideas, jump over the ***** and drop a spring on him, if you can pull that off without getting punished, keep doing it till the Marth gets annoyed and tries something else. Other idea would be to SCJ over him and follow that up with a HA, or wait to see if he tries to get you and move around him.
My only other idea would be to just ledge camp more often, making him use that technique less often. Most Marths like to push you back to the edge, but Sonic has a lot more edge tactics that most other characters, see if you can mess with him there. A stage like Halberd is a good counterpick to try because you can do a lot of planking.
Final thoughts...
If he is trying to push you back, chances are he'll dash at you from a distance to get within decent Fair range. Take this chance to "ur 2 slowe" him by rushing back, you'll have to be good to get a wily Marth with this though. Another thing maybe worth looking into is setting a spring down in his way, maybe trick him into bouncing himself? Attacking Marth from above or belove him is usually a better idea, he has a much greater chance to be life open an whiff.
Marth can be so lame to fight, btw.