The only thing is that you need a lot of coffee. And if it rains you have to apply it again. But it's greener than comercial slug repellants. There's no way I can drink enough coffee for the whole veg patch so next week I'm off to Starbucks again for some more free stuff.
I know how it works. They can't handle the caffeine. I know how I feel after 3 cups of coffee. Lord knows how I'd feel after lying on a whole bed of the stuff. They must buzz for hours! Serves them right after all my salad seedlings they've had.