Guinea Pig Odor Problem?

I use cotton rugs for my pigs and puppy pads under the rugs. Baking soda is a wonderful natural odor absorber and harmless to the pigs. Sprinkle a little bit between the fleece and the newspaper and it should keep the odor down. Some people have luck litter training guinea pigs, but mine won't use one. If you do, make sure you use non-clumping litter so it doesn't stick to them when they use the bathroom. Hope this helps a little! Good luck!