I asked this earlier and you didn't really answer. Aren't you going to have to get access to his phone to install the application? Wouldn't he know that you are installing the application even if you can find one that'll run without his knowledge?
Seems like there really isn't a way to track him via an application without his knowledge.
I think your best bet would be the Family Locator available through Verizon. You should be able to do that one without your son's knowledge. There is a monthly fee of $9.99 but you seem too dedicated for that to hinder your use (that sounded a tad sarcastic, that was not my intention).
"Peace of mind is right at your fingertips. Securely locate your family members' locations from your Verizon Wireless Device or the web. The locate feature provides you with the information you need to stay aware and stay in touch.
Provides detailed location information and the address of your family members displayed on an interactive map."
It can be found here
Hope this attempt to get back on topic helped you out.
Once again, good luck.