@hamilton,
Might I suggest a military grade microwave crowd control weapon.
http://www.wired.com/dangerroom/tag/less-lethal/page/3/
Site the vehicle at the weakest point in the place where you presently reside. Or use it to keep your escape route permanently clear of zombies wandering around aimlessly or those setting up an ambush.
Zombies aren't particularly intelligent or creatures of consciousness. Though the microwave weapon is non-lethal, the defensive effects are still whats important.
Zombies, creatures of instinct, will avoid the displeasure of exposure to the microwave field, thusly the vehicle should be situated at the weakest and most vulnerable points of ones residence/fortress. The zombies may not know or understand why but they will avoid these areas at all cost.
