The Marine Corps Hymn has been one of my favorite pieces of music since I was a kid, because my father served in the US Marines, but the logic is maybe a little questionable.
[Who are the streets being guarded from?]
The forces of evil that inhabit the bottom half of a spiritual world.
In the original version the term “portals” (a doorway, gate, or other entrance, especially a large and elaborate one) is used instead of “streets.”
I may have known your Dad.