Secure a Transparent Proxy Server

I have set up a CentOS server and configured it to be a NAT, Router, and Transparent proxy and wanted to know how I could secure it to where any request made by the client computer on the LAN side of the proxy server would be completely hidden on the WAN side so all request made would look like they were made by the server only. I added two lines to the squid.conf file such as: via off, and X-Forwarded-For off and some info is hidden but a lot about the browser and OS is still visible on the net.

any help would be much appreciated.