how to shoo a cat.

There is a cat that lurks outside my house and is really bothering my four indoor babies. This cat has taken to sitting by the basement windows and fighting with mine thru the windows and I am afraid one of them will eventually break thru and hurt themselves. Now mind you I love all creatures and now I am at a loss as to what to do. Is there something that I can get to stop the outside cat from coming around the windows and trying to attack my cats? It is really upsetting my cats who now are on edge after an encounter with the lurker cat. Twig my oldest and biggest thinks he need to defend his territory has that rage problem after seeing that other cat and is trying to attack both me and the other cats in the house. I heard there is a product that keeps cats away but I can't remember what it is called. Also I am concerned that if I use this I think it is called feline away, that it will keep the birds and squirrels away too. can anyone help me with this problem?

I have been outside three times since I posted this thread, shooing away kitties from the basement windows. Now it seems like my boys are protecting the house and sitting perched as guard cats in the window and watching every move these cats make. I have shooed them away and it seems within minutes, they are back and I am at a loss as to what to do. Gosh I realy wish that people would stop being stupid and keep their cats indoors where they belong then noone would have this problem! Don't get me wrong,I like the cats but I can't take in anymore because of a lack of room and a lack of personal "cat" spaces. I just couldn't do that to my cats, there just isn't enough room for two more(or one for that matter)in this small house. I would love to take them all in and keep them safe, but I just can't.
Their "owners" in my opinion, should not be allowed to have pets if they aren't going to be responsible for them.

Maybe some motion-activated sprinklers placed near the windows would help solve the problem??

Oh do I wish i could afford one of those. but unfortunately I can't, and we have kids that are always outside that would set off the sprinklers!LOL! I bet they wouldn't be very happy after a couple of squirts! Thanks though Lorie!

Anything citrus based tends to keep cats away. Hartz used to make a product called "No" that was pretty effective, but I haven't seen it for sale for years now. If nothing else, maybe you could have a cloth bag full of orange peels that you keep outside the window?