How to prevent a modal url being copied?

I found a snag on a membership site I’m working on:
Products have reduced prices for paid-up members. However if the url is copied whilst a product modal is visible, a non-member is able to buy at the reduced price - even though not logged in.

Ideally, when someone copies a url it would be great if it left out the product modal, like this:

Is this possible?

Update: found this and wonder if it’s OK (sits inside body tags)
oncopy="return false;" onpaste="return false;" oncut="return false;"