Starcraft – How does a Terran player stop a cannon rush from Protoss

It sounds like your problem is less, "I need a counter" and more "How could I have known?"

First off, you said you scouted him but he proxy'd his Barracks (hid it outside of his base). Let's go over the ways you could have still seen this coming:

• Usually not seeing a Barracks is a good sign he's Proxying.
• Watching for a very early Vespean Refinery is usually a sign of some sort of early Marauder/Reaper play
• Finally, many top Protoss players default into 1 Gate -> Cybernetics Core to set themselves up to stop this.

What else could you have done?

Some guide will suggest skipping that first Zealot, but if you can squeeze him out (Zealot has a 33 sec build time compared to the Cybernetics Core's 60) he serves as a good distraction to keep the reapers off your probes.

Make sure to save some extra chrono boosts to boost out a Stalker. While early game you should be using these on Probes, once you start building the Cybernetics Core stop using them and save them for the Stalker.

Another problem you had was a Bunker slipping in. There are a couple ways to stop this, but most prominently walling off your ramp. You can do this with your Gateway/Cybernetics Core, or leave space and place that first Zealot there. Alternatively, you can build an extra pylon closing off that small space with plans to kill it later.

Once he does start building the Bunker, you can use either your Stalker or even your Probes to try and kill it during production (or even better the SCV building it). The follow up will usually be a large number of Marauders so you can either push out Zealots to deal with this (its unlikely he'll have concussive shell this early), or a Sentry. With the Sentry you'll want to use force field at the bottom of your ramp to keep him from moving up and gaining sight. You can then use your Stalker to prevent Reapers from giving sight and to target the helpless Marauders.

In any case you should consider your next move. Are you going to go Robo? get out an early Immortal. Or do you want to throw up 2-3 Gate and out produce him (as he's seriously cut production).

One of the things you'll notice is that as you continue to play, the time it takes you to get out that first stalker will rapidly decrease. A Reaper rush really trades on the opponent not seeing it, and not being very experienced.

It sounds like you're building a large army and using it to gain map control, but then are falling prey to things like drops and backdooring.

If you have map control your first thought should never be: Crush my opponent, as you're essentially sacrificing an advantage (map control) for an unsure victory (because he doesn't control the map doesn't mean he can't take you). Instead your thought should be: take the map. I think you'll find this change in philosophy will lead to situations where you have a much more powerful economy than him and you're able to kill him with attrition.

Now if you're falling prey to things like BD here is a quick check list for you:

• Are you scouting? an Observer should be the first thing you build out of Robo. If you don't go Robo, a Hallucination works just as well. Sometimes scouting means sacrificing some Zealots in a pointless charge to just get inside his base.
• If you're scouting, are you seeing it coming? Overlords on the edge of your base, Starport with Reactor + 3 Rax, all of these are indicative of certain strategies you should watch out for.
• If you see it coming, how are you responding? If you have map control that means you should be able to respond quickly. Shutting down these back door attempts is often a bigger victory than a straight up conflict
• Finally, Do you have map control? If you don't have map control that means he does, and if he's beating you with map control then your problem is not "how do I deal with a base trade?" but rather, how do I regain the advantage.