Hmmm.....tough situation. Too bad the owners let such a beauty roam outside. However, to answer your question, they do sell stuff at Petco or Petsmart that is supposed to keep cats away. Maybe if you buy some of that and spray it on the porch he'll get the hint. Or, maybe you could go talk to the owners and tell them what's happening and ask them to keep kitty inside - which would be better for kitty anyway. Good luck!