Is the rule in most MD counties still just shoot at least 150 yards from the nearest neighbor's house?
Occupied dwelling. Technically if you knew your neighbors weren’t home you could shoot 50 feet from their house if you weren’t on their property.
Or written permission.
To be safe, basically ANY structure you can’t shoot within 150yds or unless you have permission. So if they’ve got a shed near the property line, don’t shoot within 150yds of it (150yds is where you are located, where your target is located and where the bullets pass through).