Getting Stray Cats to Stay Out of Yard?

I have one, indoor only, neutered, male cat. Lately, the weather here in Florida is starting to be cool enough at night to open some windows to save the electric bill from being so high, with 24/7 central air running. So, I have at least two different cats coming up to the window where my cat, Alex lays, and they both go back and forth loudly meowing and hollering at each other. My cat, as I said is fixed. Obviously, other cats don't probably know that.

But these cats are not afraid of me, and won't leave for nothing. I end up having to close the windows and put the air back on. This is OK for now, because it gets hot during the day still, but soon, when it's too cool to put the air on, then what? My biggest fear is what if these cats start spraying outside? That's going to most likely make my cat start spraying! The whole reason I got my cat fixed, was to help prevent spraying. The vet said he still can do it if he so desires. And this is not a full proof solution to the spraying problem.

So far, they have not sprayed, and neither has he. I want to know, first- why are they here? (The at least 2 different cats outside I seen coming to the windows?) 2.) are they male or female cats? Maybe in heat or something? or 3) are they looking for a fight with my cat? 4) how do I get rid of them? Without having to hurt them, of course! And 5.) and most important- how do I get them to continue to not spray? (Both, the outside cats and my indoor cat.) Please help.

This is very scary at night, with just me and my daughter home and a thin screen keeping them from popping inside. Because they sure act like they will come in if they could. Thanks for any and all help, comments, etc.

By Julie L.