Hi Heather! That's awesome that your husband is training for a marathon! Today is actually day one of my training for the Disney World marathon in January!
There aren't any defined "courses" that are that long (over 10 miles). However, there are several scenic courses, that he could use in combination with adding in some sidewalks that run along the roads between resorts and parks. Here is a link to the
jogging trails page on the Disney World website. Not all of the maps are downloadable, so you will need to stop at your front desk to get one. You can also "Google" Disney World running trail maps, and some will come up that people have posted, but they may not be up-to-date, so still ask at your resort desk.
The best bet would be to do the Boardwalk Canal Run. It will be on a map of jogging trails in the Epcot Area. It is around 7 or 8 miles and he could add a couple to it by repeating, or depending on where you are staying, he could run there and back to add some miles. I found a map of this trail on allears.net.
Here is link to a recent video that
highlights some of my favorite trails.
I hope this helps! Please let me know if you have any other questions!