add_filter( 'the_content', 'closing_shortcode' );
function closing_shortcode( $content ) {

        if( !has_shortcode( $content, 'members') )
        return $content;

        $close_shortcode = do_shortcode('[/member]');

        return $content . $close_shortcode;
}

add_filter( 'the_content', 'closing_shortcode' );
function closing_shortcode( $content ) {

        // return if the shortcode has already been added
        // Note the ! was removed
        if( has_shortcode( $content, 'members') )
        return $content;

        // Add the closing sortcode tag
        $close_shortcode = '[/member]';

       // and run do_shortcode() on the whole content block
        return do_shortcode($content . $close_shortcode);
}