Here is the current setup of the system I work with:

Internet comes in at one building where it is connected to a firewall and this goes to a point to point wireless device. That signal hits a second omnidirectional device where the signal is then transmitted to the final point to point device for the users of the local area network.

It is here at the third point that the owner would also like to have a wireless connection installed for various clients that might need internet access.

That being said, the concern now comes down to security. Said clients should not have access to any devices on the wired network, so what is the best way to accomplish this task?

Any assistance would be most appreciated, thanks in advance.