Set preferred DNS servers in Router

After every new OS install, one of the first things I do is to look for something like /etc/dhcp3/dhclient.conf and prepend my preferred DNS servers.
Sometimes this option isn't available and I've gone as far as manually editing /etc/resolv.conf and then making this file immutable (which has messed up at least one update for me).
After reviewing what I'd seen written on this topic, today I went onto my Netopia 3347nwg router and did this:
1. Enter Expert Mode
2. Click on Configure and Connection
3. Add the IP's for the preferred primary and secondary DNS servers.
4. Save and exit.

Although this sounds right and has worked fine for me up to now, I'm not sure still. My router has ALWAYS featured the ISPs DNS servers which work fine. The problem I get arises when the only DNS server chosen is 192.168.1.254 (defaults gateway). This really slows down browsing.
I really cannot see that what I did can avoid the dreaded 192.168.1.254 showing up so I don't as yet see myself getting away from prepending the preferred DNS servers.