Object over an Object

Hey Guys,

                         I'm at a tricky situation.
I have a container, a Canvas.
I have to 2 list the left-list and right-list separated by a VRule to
show a division.
In all there are 3 children in my canvas.
There's an arrow button to the left most side of the item-render-er of
the left-list.

My issue is :
When an item is selected in the left-list the arrow button should move
over the VRule.
Pro-grammatically I'm doing so, but the arrow-button seems to go below
the VRule.

For this matter I changed the sequence in which the children are added
in the container making sure the left-list
is the last child. But things are not working. Its still the same

I have come up with the conclusion that the  item-render-er is in the
list so it hardly matters if the list is the last child
to be added.

Does any one has some other solution to accomplish this??

Find the issue in the image