[JimBowy]

I want to prevent a user from getting online, but still allow them access to the local network (if easily possible) does anybody know how to do so?

The local router serves as DHCP.

[JimBowy]

I want to prevent a user from getting online, but still allow them access to the local network (if easily possible) does anybody know how to do so?

The local router serves as DHCP.

[BeerCheeze]

Disable DHCP, give them a hard coded IP address and no default (or wrong default) gateway address.

Assuming the don't have Admin rights to change it of course. Otherwise just block them at the router (either by MAC address or IP address)

[Kilamon]

Install a firewall with session authentication.