protected function _findSecondRuleKeyForHomophiles($filterModel, $bindingModel) {
        $homophileSecondRuleKey = null;

        if ($this->_isHomophile($filterModel)) {
            $bindingReferenceMap = $bindingModel->info(Zend_Db_Table_Abstract::REFERENCE_MAP);

            $foundRelevantRule = false;
            foreach ($bindingReferenceMap as $ruleKey => $rule) {
                if ($rule['refTableClass'] === get_class($this->_model)) {
                    if ($foundRelevantRule) {
                        $homophileSecondRuleKey = $ruleKey;
                    }
                    $foundRelevantRule = !$foundRelevantRule;
                }
            }
        }

        return $homophileSecondRuleKey;
    }