drow shaft plan

Well, I read through the drow argument and came up with the following.
1. Have the drow equipment not dissolve in sunlight. The whole idea was almost surely invented
for the sheer purpose of not having people run around with drow
equipment. Coming to that, if you will run around with drow equipment,
you will get yourself killed anyway. Either you'll get stoned by
villagers who recognise the make, or elves kill you. Anyone with drow
equipment will be considered drow-sponsored. Coming into an elven forest
in drow chainmail, drow dress and all will make you a pincushion.
2. My idea of the shafts looks more or less like this: Build a vertical shaft. At irregular
intervals, make hatches to stop intruders and light. The hatch will have a small (50 cm wide)
manhole in it for the operators. It will open downwards and be closed by
the operators which live in caves along the tubes. The highest hatch is
covered on the sunny side with 'Wondering Jew' type plants. On the
bottom of the shaft put 2-3 ballistae firing upwards. Also give the
operators ballistae.
Use ladders to connect caves.
Advantages of system are: 
a) Easily defendable. Ships going down will have to go throught all the
operators firing ballistae at them in a no-miss situation, while they
will have trouble manoevering and defending.
b) No sunlight coming into city.. No way man.
c) cheaper than zig-zagging shafts. Also shorter, craft can rise faster.
d) can't find it unless you know where to look for it.
What follows below is a non-scaled plan of the shaft (not more that 600 feet wide).
   
Surface      ___________________  
                 o|    |  
                  |____|o
                  |    |
                  |____|o  
                  |    |  
     ____         |    |  
  ___|  |_________|    |                Legend
C ___  H  _____________|                H - Hangar
     |__|                               C - City
                                        O - Operataror