Here is what I would do. Take the address out of the equation. Create a db set where the user creates a the links and then well they are added to the db and given a numberid or a text id. Where they can be called and instead of say
http:///blah they would see 1. Making it non forgable.
ex:
http://forum/redir_points.php?url=1 or
http://forum/redir_points.php?url=testsite
which would throw them to say
http://www.thisisjustatest.com