We have lots of fox problems on our site (see photo below captured on wildlife camera recently). So many crops have to be covered to protect them from being trampled and having huge holes dug in the beds. Poly tunnels have also been torn (even the green rip-stop type), plot holders have witnessed foxes climb right up on top then chew and tear for all they're worth. Holes have even been made right next to open doors so it isn't just to gain access to what they think might be inside.
To help deter climbing up tunnels (an act that itself causes scrapes and tears) we placed debris net screens a foot from the tunnel either side, angled outwards and slightly baggy so they can't be used as a step up. Shame the same can't be used on other net structures, blue hooped crop nets get jumped on, ran along and their wooden/cane supports bashed down or snapped.
I've tried sprinkling chilli powder and other recommended deterrents but nothing like that so far has had any effect.