No matter how many fences I put up my villagers always fall into the portal and into the nether. Is there a possibility that there is a way to turn the portal on or off? I know you basically start a fire and the portal opens. Can I snuff out the fire without destroying one of the portal blocks?
You can make a portal that toggles with redstone:
The basic idea is that you use a fire-charge dispenser to ignite the portal, and a water bucket dispenser to quench it again.
You need to use pistons to push up a block for the fire-charge to hit so that the flames are generated inside the portal frame, the water bucket dispenser just needs two quick pulses to place and remove the water block which will extinguish the portal.
You can turn off a nether portal by causing an explosion to hit any of the purple portal blocks, or by simply mining one of the required blocks.