Advice for Our Family Dog

Meet our family dog. Last June, our family rescued an adorable dog, which we named Sonic. The vet deemed him to be a poodle mix who is approximately one year of age, now two. We believe he is a mixed with bichon frise and poodle. We found him wandering the streets of our neighborhood, dirty, scared, and hungry. We did everything to find his owner: contacted a local shelter, called the police station to check if someone reported him missing, put up flyers for a "Found Dog", and used social media avenues in hope that we could find his owner. After one month, we decided to keep him. He definitely belonged to someone, as he scratches the back door when he has to go outside to use the bathroom.

To this day he is a true joy. He however, has developed a bad habit and I am seeking advice to find out how to end this behavior. He urinates when someone familiar (including my children) and visitors enter our home, with the exception of me. We have tried different methods to end this behavior; leaving him outside for a couple of minutes or putting him in his cage. As soon as he is let back in or out of his cage, he urinates. I realize that he may be over-excited, however, this must stop. He does not urinate in the house otherwise.

I would appreciate suggestions on how to stop this annoying behavior. It developed approximately six months ago. Please help us, help Sonic.