Ginger Tomcat problem!!!!?

I have two 7 year old female cats, they have both been spayed. Recently a ginger tomcat has made its way into the garden, and will moan outside my bedroom window all night long, it's keeping me awake at night for hours, so much so that I am spending the night with friends tonight in another town, just to get some peace. He has been inside my bedroom, on one night when it was warm and I left the window open, ever since then he has been back every night. I don't know what to do to deter him, he's driving me crazy. I love cats and dont want to hurt him, he has no collar and I dont know who he belongs to. Ive prayed him with water and shouted to scare him away on several occasions, but I dont know what else to do. I do not want to put anything down to deter him, as I do not want to deter my own cats from their garden, help!!!