public static function findExistingReferences($model, $field)
    {
        $invalid      = true;
        $uniqueString = null;

        while ($invalid == true) {
            // Create a new random string.
            $uniqueString = Str::random($model::$uniqueStringLimit);

            // Look for any instances of that string on the model.
            $existingReferences = $model::where($field, $uniqueString)->count();

            // If none exist, this is a valid unique string.
            if ($existingReferences == 0) {
                $invalid = false;
            }
        }

        return $uniqueString;
    }