I'm in the same position as well; especially in ZvT, I really find it hard to stop 2 base vs 3 base drops. On a map like Ohana, for example, I'll have my army just in front of the third, and then he'll drop me in the main, and then I'll send my whole army up there, only to have him dropping my 3rd as soon as I leave. Then as soon as I've cleaned it up, I find that I'm sitting at a billion minerals. o.O
You need to be prepared for this, have a plan for how to handle it. Depending on what style I am playing and the state of the game, I will leave 6-8 lings and 2 banes to defend if I leave my base like that, though usually I will have two spines and a spore covering the most critical drop area, adding spines as I get more spread out and the game progresses. This is absolutely crucial. Versus a double drop it will buy you the time you need and vs a single it can hold it entirely. Also, upgrades are super important. 10 lings with better upgrades can hold a drop alone if you are quick.
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