You can tell iOS to not connect automatically to a known network by disabling auto-join for that SSID. I do this so that it doesn't connect to "Free WiFi Secure

You can tell iOS to not connect automatically to a known network by disabling auto-join for that SSID. I do this so that it doesn't connect to "Free WiFi Secure", which can not be forgotten since it comes from my mobile operator's SIM (authenticates with EAP-SIM).