Speed Racer, I think the OP will have the barn and a B&B but the two are not necessarily related or catering to the same group of people. So, someone books a room for a night that has absolutely nothing to do with animals, horses, etc. they don't understand that a poop pile is just part of the environment.
OP, how much poop are we talking about? How many horses? How far is the barn from the house?
A couple of quick ideas:
1. Do you have a tractor so you can move the stall clean out weekly to another location that is out of sight?
2. Erect a fence on the side that the B&B guests see and plant aromatic flowers (lilacs are great and require NO care) in front of the fence.