Miner Cities are hard to build. If he has 1 Castle Archer, a few Spearton can easily get past and kill his Walls, Miners, etc. But if you gave him enough time to build 3, in essence, your opponent would have to gather 1900 gold for Castle Archers,
without building any army during this period of time. This means your army is MUCH stronger and is already somewhat completed. Attack. Really, that's all I can say. Everyone I have encountered who uses a Miner City, has lost. Also, I will show you some turtling, which didn't work at all, by the way, for my opponent.
http://pastebin.com/qX9cBXqN