Yes, you should keep the cat in. Foxes will not harm cats- coyotes most certainly will! If the critter was much bigger than a cat, it wasn’t a fox. However, if it was a shrieking fox, it may well have been chasing the cat away from its den- the foxes have just had pups this time of year. Coyotes are also denning right now, and cat is high on their list of favorite snacks. A coyote probably wouldn’t have been shrieking at a cat, it would be eating it! In addition, keeping your cat in prevents your cat from eating sleeping songbirds, picking up diseases, getting in fights with other cats, getting run over, etc.