If any person upon whom any notice as aforesaid is served shall object to any proposal contained in the notice in relation to fencing, he may, within 21 days after the notice has been served, signify such objection, in writing, to the person giving the notice, stating the grounds of the objection; and thereupon (unless the parties can come to an agreement upon the matters in dispute) all disputes, questions, and differences shall be determined by arbitration in the manner provided by Part IV .