A fast and simple response, preplace the building on an invalid terrain (terrain that you cant build on, i.e.: Water, Magma, Flagstone, Null [I know this isnt always true for null, and actually, i believe the creep will go onto the null even if you cant build on it, but anyway, NULL

] My suggestion to you is water.
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but if it is a small area like a 4x4 of invalid terrain that he wants to place it onto, the creep will still go to any valid terrain nearby. so unless you make practicallly a lot of invalid terrain, this wont work nor can melee units attack it