Guinea pigs grazing on grass are doing the most natural thing in their day, and a watching cat knows it. The answer is never vigilance alone, because vigilance blinks. The answer is a run that still works during the blink: a rigid, roofed structure a cat can land on, paw at, and circle without reaching a pig, sited where a person can see it, and used only while someone is genuinely supervising the session.
The Run Itself: Rigid Frame, Latched Lid, Paw-Proof Mesh
Build or choose a run with a rigid frame that does not flex when leaned on, and a lid that is both weight-bearing and securely latched at more than one point. Weight-bearing is the test owners skip: a cat will sit on the lid, sometimes two cats will, and a lid that bows, slips, or folds under that load is a lid that fails on the one afternoon it matters. Latches must need fingers, not just pressure, because a determined cat pats and pushes at edges until something gives, and a single loose hook is an invitation repeated daily.
Mesh must be fine enough that a paw cannot reach through to a pig resting against the side, with no torn, sprung, or wide-gauge sections anywhere, including underneath the lid line and around any door. Set the run on level ground with its base flush, so no gap opens along the bottom edge for a paw to fish through, and move it to fresh grass by lifting the whole structure with the pigs removed, never by dragging it with pigs inside. Inspect the run before every use: latch action, mesh corners, lid hinges, and the base edge, in that order, taking thirty seconds now rather than trusting last week's condition.
The Hide, the Siting, and the Supervision
Inside the run, place a solid hide house with an entrance the pigs can reach in one dash from any part of the grazing space, big enough for all of them at once without a queue at the door. A pig who can vanish completely stops being a target a cat can fixate on, and a pig who can only crouch under a see-through shelter stays stressed for the whole session. Add a second smaller shelter if the group includes a pig who gets shouldered out of the main hide, because the pig left outside is the pig the cat watches.
Site the run within clear view of the house, away from fences, bins, and shrubs a cat uses as a screened approach or a launching ledge, and out of the patrol lines cats already walk at fence height. Supervision means a person present and looking up often, not a person indoors assuming silence means safety: cats hunt quietly, and the first sign of interest, a cat settling to stare, is the moment to move the cat on and shorten the session. Bring the pigs in when you go in. A run is a grazing tool for watched hours, not an all-day enclosure, and it is never a safe overnight home outdoors.
After Any Contact: Same-Day Vet, No Exceptions
If a cat gets a paw through, onto, or into the run and touches a pig, that pig needs a vet visit that same day, even if you cannot find a wound. Cat claws and teeth leave punctures that seal over under fur while infection builds beneath, and a pig who seems merely quiet in the evening can be seriously unwell by morning. Tell the vet plainly that cat contact happened, note which pig was touched and where the paw landed, and watch the whole group for appetite loss and hiding over the following days, since fear alone can stop guinea pigs eating.
Prevention stays the whole strategy, with help held in reserve. As a fallback only, Lost Pet Alert System alerts through KinsLe reach owners close by, while anyone who finds a loose pig can message you directly.