How do I counter a zergling rush?

You have to turtle and block off your entrance. Do not use the strategy in that video. It is horrible.

As a Protoss Diamond player, I usually build my Gateway and Pylon in the entrance. I leave just enough space for a unit to pass by and I build a few Zealots to block off that narrow entrance. I also use stalkers to back up the Zealots and the Sentries to forcefield. From here, I turtle and tech up.

Terran players usually block off their entrance with supply depots (Supply depots can raise and lower for units to pass by) and a Barracks. Then they build a few marines first and then a bunker then they tech.

Remember to always scout too. Another tip is to be prepared for Mutalisks because Zerg players who mass Zerglings usually follow up with Mutalisks afterwards.

Something new players might now be aware of is how to stack scvs. Simply put, take all your scvs and send them to harvest a single mineral patch as the lings approach. When they are very close, attack them so they can all hit at the same time. Also, you might have a marine or 2 depending on the map size so put the marine in that stack as well.

Other strats :
1-Scout with the scv building your first supply depots, you will know where he rushes or not
2-Block your choke, nothing he can do then
3-Dont give up!

Many ling rushers are in fact, poor players so if their rush fails, they are both slowed by their cheap strat and in dire need of ideas about what to do next. So if you've lost a few scvs, nothing is lost, keep the choke blocked and pump scvs