BURPing

No, not the burping you're thinking of. BURP is AFOL-Speak for Big Ugly Rock Pieces.  In terms of terrain use, similarly to one-piece trees, they interact badly with the rules for damaging cover.  There is a way to get around this.  Instead of using a BURP as a single piece, cover it with smaller bricks that you can break off if and when the cover is hit by a stray attack.  Another way to use them is to lay one or two down flat -- instead of standing up like they're normally presented -- so that they look like large, glacially-deposited rocks sticking up from the ground.  Depending on the scale you're playing at they won't really be tall enough for cover.  Well, this one will be five plates tall, and the second will be seven and a half plates tall when laid flat.  The third will be ten plates tall which still counts as cover and leads you back to the original problem.