Rugby

I'm on the hunt for a specific rugby law, I thought maybe you would know. Here is the scenario.
These days when you get a penalty 15 meters or closer to the opponent's try line, someone would try to pick the ball up as quick as possible and try to score or maybe even get another penalty because the opponents didn't fall back 10 yards. But I remember when I was a kid it was quite common do a set move when you are in that situation. A penalty close to the opponents try line. One of the common moves was to build a wall. So my players will build a wall standing next to each other with their backs facing the opponents. A few guys would run a certain line and the opponent wasn't sure will the ball go left or right or maybe to the backs...I'm sure you've seen this sort of thing. But I recall that there is a law that if you build a wall like that, that the opponents are allowed to do 2 things:

One ram through the wall or tackle anyone included in the wall. I assume the argument is that one of them have the ball and that they are setting up a ruck or mall or whatever.
Or the other option was to run around the wall and try to take the ball out of the ball holders hand.

The reason I want to know the law regarding this wall is because I saw a team doing it again this weekend and the wall wasn't crushed and the opponents waited for the "move" to happen. Also the coach of the team said he was doing it whole of last season and nobody once approached the wall.

Do you know what the rules are regarding the wall, defensive and offensive? Also, would a typical level 2,3 referee know this law?

Thanks, and I hope this make sense.