This is a perfect example of how you may know 97% about what you're doing, but it's that 3% you don't know that will get you every time. Here's your simple fix: Pay a process server to serve the defendant personally. He may duck, he may hide, but eventually, they will serve him and provide you with proof of service. Good luck!
If you think my response is the best response, it would help me if you would indicate that. Also, please note that my responses to question(s) are NOT legal advice from me to you because I am NOT your lawyer, you are NOT my client, and we do NOT currently have an attorney-client relationship. Thanks!