Speaking as a hosting company... the only software I've seen work EVERY time is
http://www.proxypass.com
I don't like the fact that we can't obtain but a negligible discount on it but when clients ask me what I recommend it's the only one that I talk about. Everything else always seems to fall short on delivering. I tend to judge this type of software solution not on the 99% of the time that it is working fine but on the 1% when it is not.
Brad