Was trying to remember the trick with a block of wood to keep the window from going all the way down and coming off the track. I believe some regulator wheel on the motor assy is broken. Anyone remember the details of the wood block trick? Until I can find the replacement part.

 

I would guess that the trick would be to remove the door panel and stick in a block of wood.
www.roverlandparts.com
You can also replace the broken roller.

 

Better yet repair or replace the window regulator, it is not that big a deal.

 

That big regulator gear that the motor turns has some pretty weak welds on it. If one weld breaks it allows the regulator to loosen and run off of the motor's gear when it gets to the bottom. If that is it, just weld it back on, or maybe drill it and bolt it (I welded mine, bolts might not fit). If you don't fix it, the rest of the welds will be breaking soon and you'll be stuck.