Obviously the "obstacle" models are fragile.  Because the breakage is due to their design, if they break you will NOT get a call of "model damage" at tournaments.  At the same time, the damage is predictable (you've been dealing with it all season), so it is considered a variable for you to expect and consider while you design.  Also please understand that the models are repaired by humans...  If you see that any model isn't built correctly, Rule 19 gives you the ability and responsibility to ask that it be corrected before the match starts.