How to create fixed footer in android layout?

I am using following code to display button at the bottom of activity.

<RelativeLayout 
        android:layout_width="wrap_content" 
        android:layout_height="wrap_content" 
        android:layout_alignParentBottom="true" 
        android:layout_centerHorizontal="true" 
         >
    <Button android:id="@+id/btnGetMoreResults"
    android:layout_height="wrap_content" 
    android:layout_width="wrap_content" 

         android:text="Get more"
       />
       </RelativeLayout> 

and listview above it. when i display more data in listview this button pannel is moved down.can any one guide me how can i fix it at the bottom of activity?

any help would be appreciated.