Defending against Zergling Rush as ProtossDefending against a Zergling Rush as Protoss is more challenging than doing it as the Terran race. Protoss usually has an opening in the "wall" since none of the protoss structures are mobile. Zealots can be used to "plug" the hole in the wall commonly seen in Protoss walls.
Protoss will absolutely hate the fastest zergling rush. Why is that so? Walling in is not that simple for Protoss players as it is, for example for Terran. Terran can wall off with Barracks and a couple (or a few) supply depots. These supply depots can be lowered, but when walling the entrance to their base, the Protoss is likely to want to have an actual opening in the wall which almost defies the reason for calling it a wall.
Placing one of the units inside the opening of a Protoss wall will disallow zerglings from getting in, however, without a Photon Cannon at the ramp entrance to the base belonging to a Protoss player, a skilled Zerg player can still outsmart this scenario and break in early to chop up a decent number of probes, significantly slowing down the Protoss player.
Yes, it’s possible to block the entrance hole with a first-tier unit such as a Zealot, but remember that the Zealot unit has to use the "Stop" command. This means that the Zealot will not react to the incoming zerglings. A seemingly harmless bit of knowledge that can help the Zerg player exploit the situation. For example the zergling rush executed by a skilled player can distract the idle "stopped" Protoss Zealot by attacking the structures instead of the Zealot.
The Zealot now has two choices, either to compromise his position as the blocker of the hole in the wall and attack the zerglings or watch in anxiety as the zerglings chop away at the buildings composing the wall. Keep in mind that all of this is happening on a micro-scale. This knowledge is suitable for micro strategies but they will lose meaning in a more evolved combat situation when larger numbers of units and unit mixtures are available.
The proper way of handling a Zergling rush for a Protoss player is to use Stalkers in combination with a Photon Cannon just at the ramp entrance to your base. Blocking the ramp with units such as Stalkers may also prove to be useful but more difficult to execute than simply placing a Zealot to block a one-unit-wide hole in the wall. Remember that a Photon Cannon is the most effective way to handle swarms of Zerglings early on in the game, try building one near the ramp.