Masking logout URL

Replacing just the URL is not enough. You have to tell WordPress what to do with the new URL.

Sample code, creates a log-out URL like example.com/logout=1 and redirects to front page or custom URL after logging the user out:

add_filter( 'logout_url', 't5_custom_logout_url', 10, 2 );
add_action( 'wp_loaded', 't5_custom_logout_action' );

/**
 * Replace default log-out URL.
 *
 * @wp-hook logout_url
 * @param   string $logout_url
 * @param   string $redirect
 * @return  string
 */
function t5_custom_logout_url( $logout_url, $redirect )
{
    $url = add_query_arg( 'logout', 1, home_url( "https://wordpress.stackexchange.com/" ) );

    if ( ! empty ( $redirect ) )
        $url = add_query_arg( 'redirect', $redirect, $url );

    return $url;
}

/**
 * Log the user out.
 *
 * @wp-hook wp_loaded
 * @return  void
 */
function t5_custom_logout_action()
{
    if ( ! isset ( $_GET['logout'] ) )
        return;

    wp_logout();

    $loc = isset ( $_GET['redirect'] ) ? $_GET['redirect'] : home_url( "https://wordpress.stackexchange.com/" );
    wp_redirect( $loc );
    exit;
}

As plugin on GitHub, because this is pure plugin territory. And you cannot really hide WordPress.

it also appends title= to the end of the URL

I guess the problem is markup like this:

<a href="https://wordpress.stackexchange.com/questions/76161/<?php echo wp_logout_url(); ?> title="Log out">Log out</a>

Note the missing ".