Stray cat won't stop visiting

I have two indoor-only female spayed cats and live in a ground level apartment. There has been a stray cat (I'm assuming it's a stray but I'm not sure of its gender) coming by almost every day - mostly at night - who sits in front of our bedroom window. Sometimes he'll stand there and stare into the window (there is ledge right outside our window), other times he'll just lie down on the ground in front of the window. My one cat seems to initially take quite a liking to his visits, she keeps constant vigil at the window and I've found her scratching at the window at night when he doesn't come - I think she's calling for this cat. Now though that the weather has gotten warm, we've been sleeping with the window open (it has a screen and bars). Now whenever this stray appears and the window is open, my cat doesn't like it one bit - probably because she can smell his scent? She tries to attack the cat from our window - scratches at the screen, hissing, pouffy tail, making a big rukus. My cat calms down if you pet her and reassure her, but this has caused a big disruption in everyone's sleep - and this cat will not go away. If my cat is not at the window when the stray arrives, he'll meow and meow until she comes to the window.

Does anyone have any advice as to what to do to discourage this stray from becoming a regular visitor? Keeping the window shut is not really an option as it our only window in the whole apartment.

Hey Gracie's Mom...read this post..it may be helpful:

http://www.thecatsite.com/forums/showthread.php?t=36023

Katie

As goof stupid as this sounds, it does work IF the cat runs from humans? If he is afraid of humans then sprinkling human hair (from your local beauty shop) will keep him away. But trust me if he is pet owned, or just a stray, it won't work. He has to show real fear when you come into the room, or else you will just get strange stairs from the beuticians when you ask for the cuttings on the floor.

Another option is to go to a Home Depot and get cat proof sceens and put them in your window or buy that decorative plastic trellis that comes in sheets? They have all types and designs and get the type with small holes in it small enough the cat's can't get through the openings but air can. Cut it to fit your window and set it up so it can be easily taken down to shut the window. This keeps the cats apart, your screens intact.