How do you know it's a cat (or cats) unless you've caught them in the act? Most cats bury their waste quite carefully in any available loose soil. Foxes, however, love to mark their territory by leaving piles of mess in a conspicuous spot.
Fox mess tends to be wet/sloppy/smelly (often with fruit pips and seeds) whereas cats is usually drier and cylindrical. At this time of year, the cubs are fully grown and their parents chase them out of their own territory. You may hear them fighting around dusk time.
Then new and old territories are regularly 'marked'. Often, that's right outside my front and back doors. I pick it up with doggy bags then pour boiling water on the spot - and it makes me heave!