I got a bag type thing from our local feed store- it was sold as a "saddle bag" that goes over the saddlehorn, and is just big enough to comfortably fit one of our mastiffs without being too big. I added nylon straps to go under the belly, in front of the chest, and a snap to the collar to keep the front strap from falling down and tripping them. They are nice heavy-weight nylon with velcro closures, and have D-rings to snap the straps to. They work great on hikes, as they can carry a couple water bottles, cookies, and slobber towels too.