My sister did that at her barn too. They found some runner-type rubber mats at a flea market somewhere and put them under the porch in front of the stall doors, under the drip-line of the porch and on out in front of it for a ways. They really did cut down on the mud there too. Come to think of it, hers may have been old used conveyor belts, but what ever they were, they did the trick.
Tiff used rubber stall mats, but I'd be happy to find a cheaper substitute.