When you connect to a wireless network, your iPad (and your iPhone as well, for that matter) will hold on to that network like grim death, connecting you to it every time you come in proximity to it - whether you want to connect or not. Fortunately, it's pretty easy to stop a wireless network from connecting automatically.
- Tap Settings, and then Wi-Fi.
- A listing of available networks will appear to the right - select the one from which you want to disconnect and press the blue button to the right.
- In the pane that appears, press Forget this Network.
Now you should no longer be automatically connected to this network. If for any reason you want to connect back to the network again, you'll need to go through the connection process.