I did guinea pig rescue for a while. I kept them on
wood flake (Not sawdust) bedding. Used bedding is almost perfect
compost. If the cage is large as it
should be, 6' long so they can run "zoomies", most will use one area to potty. That makes it easy to scoop daily-ish and toss on compost bin. Most veggie trimmings go through the guinea pig first so less volume to handle and way less wild critter interest in the bin. Roll hardware clothe around a broom handle, lay several rolls on compost for air exchange as bin fills and don't even have to turn compost. Double use. And yes, they do great
lawn mowers and garden cleanup/fertilize. I used one of those portable dog corrals draped with a sheet for shade, and only when I was out there with them. You get free yard work plus a daily dose of cute! And a chance to infect neighbor minds with
reuse & no chemicals ideas because the lawn looks so good.