Big pumping systems and flood corridors are not 'simple defenses'.
Just have marksdwarves, a few tiles of fortifications, and a door. Lock the door and the invaders will stand around out front getting shot until they are all dead.
Actually, the traps are really very simple in design. My water trap actually consisted of a floodgate, cistern, and a switch. Anyone who busted in would be drowned, and the water would drain into a cistern below. Lava traps are also very simple in design. A pump, a tunnel, a floodgate and a switch, and you suddenly have the cure-all. Somethings-Awful's trap was a 7/7 magma trap that followed over the water river and came spewing out entrances, was as about as complex as my water trap. If you have to raise the lava up Z-levels, it becomes more complicated of course, but it's all simple and straight forward.