I got an idea...
Cades Cost same, more HP, and are Transcelant or w/e that big word is that I cannot spell, where they appear transperant, until a human comes by, it starts to poison him!
Like a booster... and the poison takes out % of his life, lets say 15%, and lets say aliens can WALK thru it, but when they do, it becomes deactivated for 5 seconds, and if you touch it, you take more damage from poison?
OR...
Barricades give bonus to Health Points near buildings + more HP to itself
OR...
Barricades add + 25% health to buildings or +XX% to attack to aliens that are near...
OR....
Lots of ideas, its just barricades cant suck as much as they do!