Sentries require incredibly good micro and reaction time. When I was bronze/silver, whenever I saw a sentry at the choke, I would just walk my early army back to the main, thinking "I'm never going to get past this." However, you guys have to realize that not everyone is HuK. My preferred build order against protoss is 15Gas, 14pool, 16Queen, 16Roach Warren. Push out with about 5-7 roaches (depending on what early scouting has shown me). If I see a sentry, I back off for a few seconds, then, when I think he's not paying attention to the choke, I walk my roaches up the ramp as fat as I can, and target fire the sentries. By that point in the game, I have 12 speedlings out behind the roaches. As soon as I make a small opening, walk my roaches in to make sure it can't be walled off, rush speedlings into the mineral line, and that's usually a GG. While all of this is happening, I'm building an Expo, a lair, and lots of drones. The only real way to deal with this sort of push without being HuK is to scout (if you see a roach warren, BUILD STALKERS/IMMORTALS. Do not think "Well... I can forcefield my ramp while I tech up," if your micro is not up to snuff. One tiny mistake in your micro and it's game over). Too many protoss rely strictly on micro. Micro can win games for you, but it should not factor into your strategy and tactics. You should never assume that you will win because of your micro if your opponent has flawless fundamentals. Unless you are a high diamond who can pull off a 2 sentry ramp defense flawlessly, and have a proven track record of always being quick enough with your forcefields, it's too much of a risk to rely on just that. However, if you want to tech up while being safe from attacks, throw down a forge. Two cannons plus two sentries, and you'll be secure for a while.