Running out of cash:
When I ran out of cash (which I did at the end of 2008 because of the big drop), I added more cash into the account.
I could not add enough to rebalance all my positions, so I followed the "triage" rule on page 24 of my book (5th paragraph), which is to raise more cash by selling off the worst performing stocks.
I think is it better to sell off some positions to make sure all remaining ones are rebalanced, then keeping all the positions and having them unbalanced.
This worked because I made a 44% return in 2009 (vs. 23.5% gain for the market).