just one detail, you are setting the "isavoiding" to true and in the same sub event you ask if it was set, you can actually delete that condition;
I see you created a very fluid IA, but for the effect i think a mettod where there is only needed a bullet and a rotate; at start set rotate disabled and taking angle to a position (objective). If collides with a rock, check if there is overlaping at offset to your left,if not, slow down speed while activate rotate until there is no collision in that direction, if there is an overlaping at left, rotate in the other direction. When there is no more collision, deactivate rotate, and rotate angle to objective again.
Actually they could become very smart (like a seeking missil avoiding rocks) or weird results...
ill try to recreate it and show it later