An employee is always making trouble in your company but they are not enough to fire him, what would you do to him?

After verbal warning, a written warning comes next and there is no probable cause to fire him I would put him on probation until the complaints or trouble stops. Should he do something while on probation then that constitutes grounds for determination.

 First If would be there, I will come to know whether he is a right person for the Job, if he so then observe the area of trouble and what causes trouble, if his conduct is really critical he will be sent to Training sessions and try to normalize him, as we cant fire everyone because retaining an employee is better than Fire him.