Weapons similar to metalstorm are useful for defending against projectile weapons. They create a 'virtual shield' around the vehicle. Bonus, the bullets that miss the projectile are aimed at the originator. These things seem quite robust in terms of not accidentally misfiring, or pasting some kid who threw a rock. It won't fire unless the object is moving at very high velocity.

Mind you, it would still make me nervous. Plus they're useless against plain old fashioned ballistic weapons.

As they have multiple barrels you could also build an automatic reload system that would reload some barrels while others are being fired

I've seen one Discovery show about those weapons. There really is nothing that could stop those things.

Thats why you time it. You tell the normal people 3/4 days before, the slightly gossipy ones the day before, and the true gossips 2 hours after its started.

Its also good to get a feel for how many people have actually heard about it and what the chances are of the people who have heard about actually coming. And then modify your strategy to get the number closer to the real one. One way to get more is obviously to call more people. A way to lower the number is to call some and tell them its canceled, or act really awkward about the whole thing. Awkwardness works well for a lot of things...

Your target is really the right number (and probably you should be thinking about gender ratios as well). Anything you can do to control that number is good.

The trouble with stuff like this is people are trying to throw parties and aren't watching the number.

This is a perfect example of why you don't host parties. Dane Cook, an awesome comedian, has a great bit about it. YouTube it if you're interested...