Putting on my kingpin terrorist head scarf, I'd be hesitant to operate from southern Lebanon. One, what you say makes sense from a geographic perspective. If you and I know that, then so do all the smart people looking for Zarqawi. And Zarqawi knows that. Plus, southern Lebanon severely restricts his movements. Water to the west, Israel to the south, Syria to the east and north (which has some potential for safe haven, but you've already mentioned the problems for AQ there). Jordan is fairly accessible via northern Israel, but I just don't see him penning himself in like that.
thanx for the ping