Electrical wire, a cage around it (second hand birdcages are cheap), a hose sprayer with a movement sensor..
But then again, sometimes outdoor cats just disappear. They isolate themselves when they're sick and dying. The purrrfect cover up.
I know there are some detectors available as well, that send out electical shocks to collars when animals come too close. Other than that, you could adapt it to send out high pitched anti-cat noise instead. Hopefully scaring it away every time it gets close.
You don't want electrified cats jumping around your benches..