pass url as parameter

I have a url like so

http://domain.com/track?target_url=http://www.AstonMauiLuHotel.com

I need to get the value of “target_url”

I tried using a plugin with this function to no avail

function targeturl() { $target_url = $this->EE->input->get(‘target_url’);

return $target_url;

}

anyhelp would be appreciated to how I can pass the target_url through a url.

Thanks