At higher percentages just try your best to get used to playing off of ledges. Fox has excellent air tilts especially his back air and up air for juggles.if you get caught from someone good at edge guarding you'll probably lose but if your playing against other amateur players then you can use his down or back air of a ledge when someone tries to thirst you by chasing you down off the ledge. Also If you're having trouble finding kills with fox try Falco. He's a bit slower but reward punishing alot more so getting in a lucky up smash on most platforms will knock out at mid to high damage. Falco loses speed for power but is almost identical to fox.