My granddaughter has a pet guinea pig named Chocolate Chip Cookie, or CC for short. CC has a good sized cage, but still we thought she should be getting more exercise. So we went looking at Pet Smart for a way to accomplish this and keep her safe and contained at the same time.
They had fences, plastic balls that you put the guinea pig in and tracks to roll them on, and these little vests:
CC mainly just sat in one spot looking confused. Still, a cute idea I think.