Re: Question about hay placement
Yes, pooping all over the cage seems to be the norm for guinea pigs. Some people have successfully litter-box-trained their guinea pigs but it can take time and patience and here is no guarantee that one will be successful.
I have tried various means of supplying hay for my guinea pigs: placing hay in a wire-grid-hay rack, a large, heavy crock (bowl), on the floor of the cage, in a corner litterbox, and most recently, in a plastic hanging hay/veggie feeder. I like the last one the best since it keeps the hay up off the floor and therefore it doesn't get soiled. Also, unlike the wire-gird hay racks that I have, this can be placed on the outside of the cage which allows for a little more floor space for the guinea pig within the cage. My next favorite method is placing it in a heavy crock/bowl. When I used the corner (triangle) litter box, I found that the guinea pig was using the box as a toilet. Even though the hay was changed twice a hay his feet were getting too soft from the urine and the vet suggested trying another hay holder so he wouldn't end up with foot problems. Others prefer to place the hay around the cage floor in a more "natural" manner but I have found that the hay can get soiled and I use more hay that way (which is fine if one can buy hay in large quantities such as a bale). If you do prefer to place the hay on the floor of the cage, make sure that you check the hay (and any leftover veggies) periodically so that a compost-type effect isn't being created (molding vegetation).