Living in a Bowl

have you ever thought about where you will go when the zombies start to over whelm the system that has worked so hard to hide there existence. by that time it may be too late to act. you see some time ago i realized that the valley that my town is in only has 3 ways in and out of it. highways and a freeway use the natural river beds that long ago cut the few access points to the valley. upon this realization i knew a way to keep the whole place safe. you see with out those points of access the valley is really one big bowl. even the freeway needs a bridge to get over the tall peeks that surround the town. how easy it would be to close them up in an emergency. Zombies (walkers or runners) lack the fine motor skills to clime, so going up the mountain would be nearly imposable for them. however if the zombies did manage to scale the mountains the drop into the valley would either destroy them, or cripple them to allow for an easier kill.
yes i know its a lot of work. i know it would take a lot to convince a whole town to cut off its only way out. i cant however ignore the Chance it might give my town, family and I to survive an event as horrible as a Zombie fulled end of days.