Wow! Thank you all so much for the suggestions and advice (keep 'em coming, if you have more!). I knew I could count on Pet Talkers! It is so incredibly helpful to know that this is not an isolated problem and that others are dealing with it too.

Yorkster, thanks for the tip on outdoor repellant spray; I'll look for some at Petsmart. And Purrley, I'll let you know how it works!

I do see a pattern forming here that has to do with abandoned strays and their later behavior. I agree with Yorkster that whatever happened earlier in their lives to affect their current behavior is not their fault. I think my Emmett, like Purrley's Panda, is grateful for what he has now and is trying to defend it from "invaders."

Anyway, thank you all again for your help and advice. (Big sigh of relief!!)

Cindy, Stump, and Emmett