How can this this URL Checker be made cleaner?
one line functions make your logic hard to follow, I would advise strongly against them.
Especially if you only call that function only once, which is the case in most of your code.

As a very minor comment, I would put 

curl_setopt($this-&gt;curl, CURLOPT_NOBODY, true);
curl_setopt($this-&gt;curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($this-&gt;curl, CURLOPT_FOLLOWLOCATION, true);   


inside __construct(), it should be a tiny bit more efficient.

One more minor comment, $url could easily be passed as a parameter, why make it a property?

All that taken into account, I would rather maintain something like this:

class URLChecker
{
private $curl;

public function __construct()
{
    $this-&gt;curl = curl_init();
    curl_setopt($this-&gt;curl, CURLOPT_NOBODY, true);
    curl_setopt($this-&gt;curl, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($this-&gt;curl, CURLOPT_FOLLOWLOCATION, true);    
}

public function __destruct()
{
    curl_close( $this-&gt;curl );
}

public function URLisValid( $url )
{
    $httpcode = $this-&gt;getHttpCodeForURL( $url );
    return  $httpcode == 200; //HTTP_RESPONSE_OK
}

private function getHttpCodeForURL( $url )
{
    curl_setopt($this-&gt;curl, CURLOPT_URL, $url);
    curl_exec( $this-&gt;curl ); 
    return curl_getinfo( $this-&gt;curl, CURLINFO_HTTP_CODE );
}
}