Well, actually I disagree with you Domo. If he can change its size and length and such, he could turn a pebble into a boulder. However, since he can't changes its weight nor its mass, that boulder is still gonna weigh as much as a pebble, and be as dense as a pebble (considering a pebble is what he uses his powers on in the first place). So basically, whether he turns the pebble into a boulder or a towering pillar, those items are still only as dangerous as the item it was originally (in this case a pebble). When he gets a higher rank, maybe then he can learn to add mass or weigh to these rocks, at the cost of chakra and such. But, I approve.