The Dan's Guardian package is the only way of doing that I'm aware of. I have no idea how stable or unstable it is, there is a thread on the packages board on it.
Thanks all for your efforts for explaining, but my requirement is different and I am using squidguard. This topic went to Dans Guardian, which is different squid server, which i need to configure completely from scratch. I requirement was to block the users when the users is just typing the search catogory, which should get blocked at the sametime when is has pressed enter. And it seems it does not works with a squidguard, it just works with Dans Guardian.
Is there any way that I can use both at the same time?