Any person who keeps a dog which is generally considered to be vicious, for the purpose of protection, shall acquire a special license therefor from the county assessor. The assessor shall charge $10 for such license. Such license shall be required in addition to the license required under section two of this article. The keeper or owner shall properly secure such dog in such a manner so as to prevent injury to a person who lawfully passes through or enters upon the property of the keeper or owner. Nothing contained in this section shall constitute a defense to any action for personal injury, wrongful death or damage to property.