Short answer (on the switch):
- Disable all ports that aren't connected device receiving a reserved IP
- Setup port-security using sticky macs
The following commands will set an interface to allow only currently connected device to use that switchport:
switchport mode access
switchport port-security maximum 1
switchport port-security mac-address sticky
This is a 2 part problem. Part one assigning addresses, part to disallowing access to computers not assigned a "reserved address" in DHCP from the sonic wall. I think you've got part one solved on your sonicwall. The second part needs to be solved on your switch.
Like @Tom Shaw said using port-security command on cisco switchgear is a good idea. However it's incomplete you need to specify the max number of devices MAC addresses that can come from that port
switchport port-security maximum 1 (provided there isn't another a switch or hub hanging off that port).
To save yourself from having to type in MAC addresses you can use
switchport port-security mac-address sticky after you've turned on port security. to add the MAC address of the currently connected device to the approved list without having to type it in by hand.