Hi @flowers1 , could you please elaborate on the issue?
With the standard modem, I am sorry to say there isn't much you can do as the port is open to anyone. What you can do is to get the MAC address of his devices and put a time filter on that MAC address. You can set filter to have access during a particular time or NO time at all under Parental Control. Remember to change the modem's default password so he can't go in to change the filter/rules.