The county clerk on his own initiative or upon order of the board of county commissioners shall at all times have authority to conduct investigation and to make canvasses of the registered voters in any precinct canvass or at other times and by other methods than those so prescribed. However, the county clerk shall conduct a verification of voter registrations at least once in every 2 years, and shall cause the cancellation of registration of persons who have ceased to be qualified voters. Such verification shall be accomplished by one of the following methods: (1) precinct canvass conducted by 2 qualified persons of opposite party affiliation appointed by the county clerk or (2) written request for verification sent to each registered voter by first class mail, not forwardable or (3) an alternative method of verification submitted in writing to and approved by the State Board of Elections at a public meeting not less than 60 days prior to the date which the county clerk has fixed for implementation of that method of verification; provided, that the county clerk shall submit to the State Board of Elections a written statement of the results obtained by use of such alternative method within 30 days of completion of the verification. In each precinct one canvasser may be appointed from outside such precinct if not enough other qualified persons who reside within the precinct can be found to serve as canvasser in such precinct. The one canvasser so appointed to serve in any precinct in which he is not entitled to vote prior to the election must be entitled to vote elsewhere within the ward or township which includes within its boundaries the precinct in which such canvasser is appointed and such canvasser must be otherwise qualified. If upon the basis of investigation or canvasses, the county clerk shall be of the opinion that any person registered under this Article 5 is not a qualified voter or has ceased to be a qualified voter, he shall send a notice through the United States mail to such person, requiring him to appear before the county clerk for a hearing within ten days after the date of mailing such notice and show cause why his registration shall not be cancelled. If such person fails to appear within such time as provided, his registration shall be cancelled. If such a person does appear, he shall make an affidavit similar in every respect to the affidavit required of applicants under Section 5-16 of this Article 5.