Ok, first off: show that you have the correct paperwork and the like to show that yes, the fox is your's.
2nd: contact the local humane society and have them check your home, and explain about the medical conditions the fox currentally has and what you are doing to help it.
3rd, if nessessary: Make sure you have a legal counsel available just in case.
Also, a quick google search brought this up, so it may help some too.