Neighborhood cats shit right in the middle of my lawn. It stinks and the robot lawn mover makes it even worse.

I do NOT like cats, and this is not helping.

What works to keep them from shitting on my lawn?

The votes have spoken. Some people are cat lovers; thanks for the great advice from the rest of you! I will not go out of my way to accommodate other people's pets that aren't welcome on my property. My first weapon of choice will be chili because it's simple and cheap. Other ideas have been noted.