I think the best way is to block these kind of sites by dns filtering. First you need to setup a transparent dns redirecting:
/ip firewall nat
add chain=dstnat action=redirect to-ports=53 protocol=udp dst-address-type=!local dst-port=53
add chain=dstnat action=redirect to-ports=53 protocol=tcp dst-address-type=!local dst-port=53
of course protect the router from outside dns requests
/ip firewall filter
add chain=input action=drop protocol=udp in-interface=WAN-interface dst-port=53
add chain=input action=drop protocol=tcp in-interface=WAN-interface dst-port=53
After that, you either create your own dns server with your filters, or you rely on services like opendns.com and set the dns of router accordingly.
This way all dns requests from LAN will be redirected to the router dns cache, which in return will request to the dns server of your choice which does filtering.
And a Happy New Year