See how they're going for the ledge. If they go low, you can either:
- do the Marth-killer (stand with your back to the ledge, and light-shield, having the shield face the ledge)
- Drop-zone bair stagespike (Not recommended. But some fall for it. Run off the stage and perform a back-air right next to the ledge. If you time it properly, then at high percentages, it will stage-spike them. Assuming they are at a high percentage, as you knocked them off the stage. Not recommended, because they can tech it, then they will get back to the stage, and you will have to up-B. Because Marth is Marth, they'll probably edge-guard you for a punish. I do this to a friend who isn't good at teching, and it always works for me. If/when he learns to tech, I'll have to stop. On the other side, this is a great mix-up, as other Foxes never go for this option. Very unpredictable. Not very viable at high-level play, unfortunately.)
There are more ways they'll go for the ledge, definitely, but they'll usually go for a sweet-spot, in which cases, you can go for these options. If they don't go for a sweet-spot, that's their problem, and you can punish.