You can and should fire him. You risk liability yourself if you continue to employ a handy man who trepasses in units and assaults residents.
Whether or not you owe him for his "extra" work will depend on what he can show he did, what he can show he spent, and how your agreement of repairs for rent is worded.
You can reach Harkess & Salter LLC at (303) 531-5380 or info@Harkess-Salter.com. Stephen Harkess is an attorney licensed in the state and federal courts of Colorado. This answer is for general information only and does not create an attorney client relationship between Stephen Harkess or Harkess & Salter LLC and any person. You should schedule a consultation with an attorney to discuss the specifics of your legal issues.