Most of these suggestions, are not even practical on heavy clay soil in our barn yard. I can not let the horses out to pasture in the spring time, until things start drying out, I do put old straw and sawdust or wood chips in the worst areas, but I wish I had better means of caring for the horses when "mud season" is here.
Adding organic material to the mud like hog fuel is cheap, but very temporary. Eventually it breaks down and makes more mud. And if you try to put landscape fabric underneath to prevent it from mixing in with the mud, the joke's on you because once there is mud on top of the fabric it is insanely hard to get the stuff out. And you will want it out because loose ends of fabric that come up out of the ground can pull off shoes and catch on tines of your muck fork.. Not that I have made these mistakes before ;) This is what we use on our boarding farm: Lighthoof Equine Mud Management Panels. Video and info at http://www.lighthoof.com We install it just in the front of our paddocks where the worst mud is. The horses actually prefer to stand on it which reduces the wear and tear on the rest of the paddock.
For most arenas, topsoil, footing, and base layers all become compacted over time. This is because the more often the area is used, experiences difficult weather, and simply ages over time, the more different layers of your arena bleed into one another. This makes all layers less effective.