I think there are two sides to this coin. Mang0 was pretty stubborn for a long time vs Armada, and would always run in and get punished so much that he considered him a 'brick wall'. He mentioned how he had to accept the fact that you have to camp peach with lasers and approach wisely, so this playstyle will be very common vs peach players.
So now, every time that Armada plays defensive vs mang0, you generally see him retreating to camp lasers in order to get Armada out of his shield or defensive stance; obviously its hard to see it in action cause mang0 is so fast, and he switches very quickly between camp and approach, but other foxes aren't as fast.
What Armada has to do instead is to be aggro, and zone out the fox from the stage. I think peach struggles in this more than most top tiers definitely, but its very much doable. F-air will trade in peach's favor vs fox's nair or bair, unless the % gap is clearly different, so go for trades whenever you can, since peach is the queen of trades. Thing is, Fair takes a while to come out, so if theyre stuffing you with aerials before your Fair comes out, then you have to do it earlier. If it doesnt hit u can cover yourself with jabs if the fox goes for a grab. (assuming u fastfall and jump cancel it)
If the fox is running, he only has so many places to run to. You can create a wall of fairs in his direction (or something similar), and eventually force him to lose his ground. But you have to be smart on this because some foxes are trying to bait out your moves to punish. Like a marth would do, you have to shove him away from the stage and corner him to limit his options, or fight back on his approaches with your turnips and dash attacks.
Dont commit to approaching, but rather commit to zoning him away safely, and break his dash dancing and space with your dash attacks and turnips. Eventually u can spray the fox once you corner him.
EDIT: just saw this set on salty playground, i think game 2 is a pefect example of how to handle fox camping
https://www.youtube.com/watch?v=hy4yP7uZNxU (bonus phantom stitchface!? :V)