PHP检测国家而不管代理

I would like to detect a user's country or country code regardless if they are using a proxy. I don't necessarily need to use PHP to accomplish this. I was hoping I could pull out a constant from the computer and I'm not very knowledgeable about proxies. The end result is to block anyone from ordering from my store who is not sitting on a computer in the US. Thank you!

You can not do that.

• You can't be sure what country from is user
• You can't be sure if he is using proxy
• You can't be sure if he is using computer device
• You can't be sure that he is human.