Dynamic Integer Arrays - Play Random Cells

In the player vs computer tic tac toe game I've been working on there are 2 boolean arrays (one for the computer and one for the player) that track which cells have been taken. When all other moves have been exhausted I would like the computer to play a random cell. To do this I am trying to gather the indexes of all False values from the 2 arrays and add them to another dynamic integer array. The computer will then choose randomly from the new array. The two Boolean arrays are plyrTaken and cmptrTaken. The dynamic array is occupied.

Here I declared the arrays:
Public Class Form1
Private occupied() As Integer
Private plyrTaken(8) As Boolean
Private plyrPairs(14) As Boolean

Here I got the dynamic array ready for use:
Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs) Handles MyBase.Load
ReDim occupied(0)

And here is the code I have attempted:
For index As Integer = 0 To 8
If plyrTaken(index) = False And cmptrTaken(index) = False Then
ReDim Preserve occupied(UBound(occupied) + 1)
[Code] .....

In the last block of code I was just trying to print the contents of the array to a list box so I could see if it was working. Obviously, it's not. When one position is occupied the list box shows the occupied cell index with a Zero. This really shouldn't be there as I want only taken cell indexes to be sent to array and list box. When a second position is occupied 7 zeros are added to the list box. Kinda shows promise as 9 total cells - 2 is 7 but there should be index numbers other than zero to represent the cells that have been occupied.

Also, the indexes shouldn't keep adding on to the dynamic array I need a way to clear the array and resize it back to 0. I tried adding
Redim occupied(0)
to the top of the code but that didn't seem to work.