If there's a seasonal product on your bike that you probably ought to have, the guys at Portland Design Works most likely make it. Fenders on fat bikes don't seem like a must have until you take one out on the trail or on the road and there's a bit of water, slush or snow out there. Those big tires grab all that gunk and throw it up at you with a vengeance. The Mud Shovel fenders are there to keep that mess off of you and your bike. Add in a little bit of salt in the winter climates and you can see why these are a must have.
From the modest folks at PDW
The original fat bike fenders! The Dave's Mud Shovels are designed specifically for fat bikes - they're extra long and wide to block the snow, water or sand you'll ride through on your next fat bike adventure. Made of heavy-duty polymer, the Dave's Mud Shovels are super lightweight but sturdy enough to take years of bad weather abuse.
The front fender mounts to the downtube of your bike using adjustable rubber straps for a secure fit. The rear fender mounts in seconds to your seatpost for easy on/off depending on riding and weather conditions.