If you don't wish to see the topics which are posted in various boards there a couple of ways you can do this.
Firstly if you want to hide all the non-dog related boards go to the Board Index
and click the "minus" icon next to the Other Boards
heading. The individual boards within "Other Boards" will no longer be visible and furthermore when you use Active Topics
you will see no posts from any of these boards.
If you want to be more specific and want to exclude certain boards use the Options
link and then the Boards
link. You will see a list of all the boards and there is a "hide" checkbox which will remove those specific boards from the Board Index and Active Topics.
If you have removed a board and want to see it again simply reverse the steps above. And you will always be able to see the full list of boards on the Forum Home Page