xset +fp /usr/share/fonts/local
and try
urxvt*font:     -*-terminus-medium-r-*-*-12-*-*-*-*-*-*-*
again. Works for me :-)
You need to add 'xset +fp /usr/share/fonts/local' to your .xinitrc or add that fontpath to xorg.conf.

Edit: I'm not sure if it makes a difference, but you can try disabling antialias:
urxvt.font:             xft:terminus:antialias=false:pixelsize=12