Ways to stop stray cat spraying on our deck?

Let me get this straight......you want something that will scare the stray cat, but WON'T scare away your own cats? That's near impossible. Your best bet would be to get a live trap, set it, put a can of tuna, or some cat food in the back. When you catch him, take him to a place that will spay/neuter feral cats for free!