Synchro wear doesn't actually cause gear pop-out directly. Worn synchros will eventually lead to crunching gears (actually it's the male dog ring teeth that clash with the shift sleeve slots to cause crunching) because the synchro has lost its ability to match gear shaft speeds for the teeth to engage the sleeve most easily. Gear crunching as a result of worn synchro bands (and/or shift sleeve) can be reduced almost entirely by slowing down your shift or double-clutching. But ultimately parts need to be replaced to eliminate the crunching.
Gear pop-out can be loss of dog ring teeth. That's why Peter said check the drain plug magnet for lost teeth stuck on there. The loss of those teeth prevents the gear from remaining engaged within the shift sleeve when power is transmitted through the gear. Or the shift fork is out of alignment and the teeth are not fully engaging the shift sleeve.
The exploding synchro saga is typically due to the synchro being forced to do too much work. Usually too worn to do it's job and actually its too much force put on the synchro & gear when coming OUT of gear. That force is caused by yanking on the shifter before the clutch is fully depressed and disconnecting power from the gear stack. Premature yanking (keep it clean, this is a family show.....) makes the big flat retaining clip flex and eventually can come off the gear. Once that clip lets go, serious carnage ensues. The trick to fixing that is converting to 930 retaining system. But that's only directly changeable on 3rd & 4th. 2nd isn't possible w/out modifying the gear.
http://forums.pelicanparts.com/porsche-911-technical-forum/753069-915-4th-gear-issues.html