If Marine line units need this kind of reminders, the same is probably true of the Army as well. The infantry fieldcraft has degraded so much that we are failing in defensive positions. That is disturbing and sad.
It is sad because the US Army infantry, in the days of WW2 and Vietnam, used to be great in the art and science of Defense. They'd go somewhere, set up for the night, and wait for the enemy attack. When the enemy do show up for the inevitable attack, the GIs would hold the line, and call in artillery, our technological advantage.
If you know someone deploying in a line unit, please send them a copy of Command Legacy. It's a great follow-up to FM 7-8 Infantry Platoon.
Yes, your defensive positions have to make sense. You need supplementary and alternate positions. And you need to check your positions and call on your neighbors.