My guinea pigs live in the backyard. They have cages that they can go into if it gets cold - but generally they roam around free. They mow the lawn - so we dont need to cut it very often. They are very territorial so they dont try and leave the backgarden. You just have to separate the males and females or get the males desexed - otherwise they breed rapidly.

Guinea pigs have interesting social lives if allowed to free range.

We dont have foxes ( not many) and cats do not seem to bother them. Currawongs have been known to chase them though.