How to disconnect JavaScript popup from opener

How to disconnect JavaScript popup from opener

I'm opening a popup from my main page with code like this:
<a href="http://external.domain.tld/"
onclick="window.open(this.href, '_blank',
'width=512,height=512,left=200,top=100');return false">
Open popup
</a>
This works fine, but my problem is that the document which is loaded in
the popup window has the permission to change the location of the opener
window. This even works when the document in the popup is from a different
domain. It has no permission to read the location but it is allowed to
change the location. I don't want that. I want the popup to be completely
disconnected from my main page.
Even without JavaScript it doesn't work. When I open the other page in a
new tab by using the target=_blank attribute then this tab still is
allowed to navigate to the opener window and change its location:
<a href="http://external.domain.tld/" target="_blank">
Open in new tab
</a>
You can see a live demo here. Click one of the two links to open an other
page in a popup or a new tab which then loads a third page in the opener
window. That's what I'm trying to prevent.
Is there some trick I can use to break the connection between the opener
window and the opened window? Ideally the opened window should not know
that it was opened by any other window at all.