I have found it is a good idea to send a marine to each empty hive right off the start of the game (provided u are in a large game, around 8 each team). Very often they will encounter a gorge walking up undefended, and killing him will slow down the alien progression immensly early in the game. Make sure they are smart enough to stand at one end of the room. It is very tricky for a skulk to assault a marine doing this, I can hold a hive like this for a good 5-10 minutes against several skulks, provided the comm drops me health and ammo once in a while.
Get off my plane.