[villagetinker]

I came across the "2 foot rule" but this was in a discussion with a next door neighbor, and it involved the swale between the houses. This previous neighbor was thinking of a common landscaped area that would use alternating tree/hedge to provide privacy between the back yards.
When I called ARC, they told me under no circumstances could any garden occupy the swale area, the reason being that during periods of heavy/very heavy rain the land scape material would wash away into the drainage system.
So, if the new landscaping is in a swale area between your houses, it will probably need to be removed (the start of the war??) however, the landscaper should know the rules.

By the way we did discuss the problem with mowing a piece of lawn 2 foot (4 foot total), we gave up on the idea, and that neighbor has since moved.

Hope this helps.