x-country fitness?

I'm getting back into Eventing with my jumper dressage horse and wanted to know if you guys had any tips for preparing for the x-country.
We live in Florida and have absolutely NO hills :( and not many trails nearby. I need some good exercises that can be done in a 5acre field to improve my fitness as well as my horse's.
Any suggestions would be great!

There are a lot of different exercises you can do to increase your horse's fitness level that doesn't involve hills. I love this book:

Amazon.com: Equine Fitness: A Program of...
It has punch-out cards for each exercise that I ended up getting laminated so that I can plan out a few exercises before I leave my house and bring them with me to the barn. It also has some great detailed plans on how/when to utilize the exercises.

I also just started a thread called "New to Eventing - Tips/Advice" where there is a suggestion for building up endurance to navigate a beginner course.

Double lunging:) do it for 10 minuets a day. I also do free jumping in a safe closed arena.