How can you stop someone from tagging you in a picture on Facebook?

You can't. You can make your tag photos for only you or you can block the clients from seeing the tagged photos album.

This how do it .

Go Setting --> Privacy --> Profile

Otherwise You Can Go Directly clicking This

http://www.facebook.com/privacy/?view=pr…

Then you will display like this

Choose as i done.

And Click Svae Changes