Restricting sites with mikrotik

Hi
I use mikrotik as my internet gateway and firewall and also to manage bandwidth for myself and clients. I want a situation where i can restrict certain websites from opening using the mikrotik gateway on just one network out of the 3 different network the mikrotik is serving as gateway.please hw do i achieve this?
Thanks

Just use webproxy or proxy and set your ACL

Maxi

my box is set up with 3 lan cards. one for my isp, one for my network and the last for clients i serve. now if i enable web prooxy or proxy and restricts those site won’t it affect my clients network? cos i only want the restriction on users connected to my own card alone.
considering the fact that NAT is enable on the first card.

Thanks.