The infinite falling blocks projectile problem.

Please help me, i have made a modd with a projectile that makes a trail of falling blocks that are yellow carpet(don't question it) but if you throw it straght up, once it loses all its momentum it just hangs in the air, makeing carpet, then the game crashes after a wile,I came up with a solution, if it is not travaling on the X or Z axis, it spawns the carpet one block lower. However, that is suprizingly hard to code, any ideas?