I've been caring for three 1/2 (and a half because one comes for food only) cats outside for three years. All four were neutered and we've set up shelter in our garage. In addition, I have four cats inside. There have been cats that occasionally stop by, but none have remained. Earlier this summer, a big male cat began coming around. He started spraying in and around the shelter area and chased my sweet outdoor male cat (who is best buddies with the other two females) away. Now PJ, the male, hardly comes home. This new infiltrator is trying to move in. I tried preventing him (Mr. Gray after Stephen King's character) from eating their food by standing there while they eat and taking away their bowls afterward, but this cat just won't move on. He (Mr. Gray) is getting thinner and it's upsetting since I feel for any cat and he seems nice to me and is very handsome. Last week as he walked past our door, one of my inside cats (female) burst through the screen in attack mode. Thankfully, she just chased him away and we were able to get her back inside. Now I'm nervous about having the doors and windows open. I really don't know what to do. I'm at my wits end. I haven't seen PJ for two days and I'm worried about him. Also, I'm off for the summer and can more easily deal with the problem, but I won't be able to stand guard once school starts. Ideas?