Okay, but if you don't have a weapon capable of putting an end to the Enemy, ultimately it won't matter whether you have failed to make it invincible or not. It's "vincible," in that it can be conquered somehow... but you don't have the means to conquer it with.
Ultimately, if you're trying to confront an enemy rather than hide from them, your first priority must always be intelligence as to the nature of the enemy, and your second priority must always be a weapon capable of harming them.
If all you want to do is hide, you can skip number two.