Personally I use runaround stuff. I use this
http://www.runaround.co.uk/collections/connections/products/connection-kit-4, then I can shut them in the run if I ever need to catch them for the vets and they're hiding in the run :lol:. I have two tubes joined together to allow me to move the run around to fresh grass every few days, as with two of them there's a lot of stretch and bend! There's a cheaper kit though if you just want to attach it and not move it:
http://www.runaround.co.uk/collections/connections/products/bridge-link.
The runaround stuff is very secure, I really don't think there's any way a fox could chew through the pipe or break the flower part. It's also very easy to fit - all you need to do is snip a hole in the mesh with wire cutters. You can attach it to the wood of the hutch if you'd rather, but mesh is easier if you're not too DIY savvy!
I've also seen this but never personally tried it:
http://www.boylespethousing.co.uk/accessories/joining-tunnel.html