At any time before final order or judgment against the garnishee, the defendant may in all cases, by answer duly verified defend the proceedings against any garnishee, upon the ground that the indebtedness of the garnishee, or any property held by him, is exempt from execution against such defendant, or for any other reason is not liable to garnishment; or upon any ground upon which a garnishee might defend the same; and may participate in the trial of any issue between the plaintiff and garnishee for the protection of his interests. The garnishee may at his option, defend the principal action for the defendant, if the latter does not, but shall be under no obligations so to do.