How can huge bubbles in pizza crust be prevented?
From Encyclopizza


  There’s a difference between bubbles
  formed from under-proofing versus
  over-proofing. Bubbles from
  under-proofing tend to be flat but
  large in diameter. If unpopped, they
  can blow up an entire pizza. This is
  the process by which pita or pocket
  bread is made. Bubbles from
  over-proofing tend to be high but
  smaller in diameter. They rise up like
  little ping-pong balls and eventually
  form a hole at the top, at which time
  they stop expanding. They almost
  always burn. Most pizza bubbling
  problems are of the under-proofed
  type. 
  
  To resolve a bubbling problem, dough
  fermentation must be adjusted
  accordingly. To stop bubbling caused
  by under-proofed dough, increase the
  amount of fermentation. To stop
  bubbling caused by over-proofed dough,
  reduce the amount of fermentation.
  
  In addition to proper proofing, it has
  been found that reducing the amount of
  water in a dough formula can help with
  reducing bubbling when dealing with
  the under-proofed type. The reduction
  in moisture aids in creating the
  pinpoint holes in the cells walls.


In addition, you want to make sure you properly knead your dough. Some people poke tiny holes in the dough to prevent overly large bubbles. As a final resort you could observe your pizza in the oven and poke bubbles as they form.