Free roaming near Zone 2

[#1]

While on a Greek island close to Turkey, my Android mobile phone switched momentarily to a Turkish provider (zone 2) and I was charged over £3 for data roaming. The Welcome SMS from the Turkish provider alerted me and I switched off roaming immediately but I see now that the phone had already used 50MB in the background. Is there a way to have roaming on for EU countries where it is free, but off for neighbouring countries where it is not free? Surely, locals will have this problem all the time. 

Thank you.

[#2]

locals won't have the issue as they won't be roaming, because they will be in their home country they can switch roaming off.

there's now way to roam specifically by location that I know of - it's all or nothing.

[#3]

In settings I believe you can select preferred or allowed networks the phone will connect to. I considered experimenting with these but I thought that might break my setup. Another possibility would be an app if Android allows such low-level control.