how do i permanently block pop ups for certain sites

According to this thread > http://www.techsupportforum.com/forums/f65/blocking-individual-web-sites-on-safa ri-226175.html

You can use the Terminal app to block individual sites but be aware, unless you are familiar using Terminal, best to click your Apple menu (top left in your screen) then click Block Pop-Up Windows from the drop down menu instead.

If your version of Safari can run extensions, the JavaScript Blacklist extension blocks javascript by domain.