Nice thought, but i doubt it would give any benefits
In case of an alien invasion, i guess, we'll have to assume, that they're somewhat ahead of us on a technical level, with interstellar / -dimensional travel available and such.
So question is, what would trigger an invasion ? Ground ? People (for whatever reason) ? Resources ?
If they'd need our planet to habitate, they would be here for a longer time and you couldn't store enough food for this time. If it's people, well, being technological advanced, they would find you. Even by our standards, there's just no way to hide - given all the available surveillance technology. And finally, if they're here for the resources, you wouldn't be of interest
. In case of war, what do we have to thwart an invading force, that could be hundreds or thousand years advanced ? Would a few of todays armed forced be able to stop an entire medieval army ? I think, they could and that throws us into a scenario, where nothing we have could seriously harm the invaders.
