What type of router are you using? Can it support VRFs or multiple VLANs? VRFs can also be used to segregate trafffic inside your network, however you will need multiple internet drops for this. Using VRFs is a great way to separate your guest network within another network.
On your switch and router, you can create a guest vlan, and map it to a SSID on the AP. Then users who connect to this SSID will also be mapped to this VLAN.
If you have a single internet connection, then you will need to create ACLs which prohibit this guest vlan from being routed back into and able to talk to your corp vlan. ACLs can accomplish this
For how-to help, please consult the config guides.
HTH,
Andrew Lissitz