>Also, the floor vents are NOT secured in any way and are an EXTREME DANGER
>to any unwitting ferret who decided to see what is in there.  We all know
>that would be high on a ferret's agenda on what to check out in the new
>house.
 
I have the same problem, and have sort of solved it by making sure
something heavy is holding each of them down, like a table leg, a chair
leg, a heavy vase, etc.  Not the answer you were looking for, probably,
but keep in mind that dirt, dust, fur, crumbs, etc.  fall into those
vents.  It's helpful to be able to remove the grates for cleaning every
so often.
[Posted in FML issue 3554]