[1] Doc Tornado as high as you can.
[2] Rising pill jump towards the edge (if you're high enough you can throw multiple pills)
--- This is the most important part if you want to avoid getting hit by Marth's F-Smash. Remember to throw the pills at them. They'll have to bypass the pills in order to even touch you. This is best against Marths, and edge-guarders that like to hang out on the edge.
[3] Then, you'll want to sweetspot the edge, so you'll need to come from underneath. If you need to cape, do so (however I like to save those).
[4] Hopefully, those pills you threw earlier should keep them preoccupied while you approach the edge. Proceed to sweetspot the edge. You should get safely on the edge if Marth is edge-guarding the conventional Marth-method. If the Marth player has good timing. Then you can tech off of the edge.
This isn't perfect, but it certainly keeps you alive longer and forces the opponent to kill you like a man on the stage. This works well against Taj's and B-Will's Marths, so I know it works. However, they usually kill me on the stage anyway. They're too good. But, yeah, I get tons of kills coming back to the edge.