Keep track of the path with instance variables, for example give the grid a cooldown variable.
Then before picking a random instance, pick instances which have cooldown = 0.
When the ball moves to a spot, give that spot a cooldown variable of two (if it should not be allowed to move there the next turn, but the following turn). At the end of the event you pick all instances with cooldown > 1 and substract 1 from them.