Block Port 53 - BT Business Hub

[#1]

I have a BT Business Hub and would like to block Port 53 for outbound traffic. This is to prevent users circumventing the OpenDNS rules I have set on the router by changing the DNS on their individual devices. 

I have logged onto the Hub Manager, and gone to Custom Configuration. However I get a message, "Firewall custom configuration is not available if Static IP is disabled".

I am not sure I am going to the right place to block the port. Would appreciate any help!

Many thanks in anticipation

[#2]

Have I put this on the wrong thread?
Loads in here about the BT Business Hub - can no one help with this?

[#3]

Moderators Note

This topic has been moved from Fibre to My Router