Biff bars or anti-biff bars, now I know what they're called and what they were supposed to do and I'll definitely be able to sleep easier tonight! Thanks for the information.
As for the name, I could imagine that it was derived in one of two ways:
1) Pinball player named Biff, strolls into his local arcade back in 1955 and fires some quarters into his favourite machine. He death saves time and time again and is going crazy on the machine, and the local patrons are casting a rather evil eye Biff's way. The owner sees this and walks up to Biff and says "my goodness Biff, would you just take it easy on that machine?", to which Biff replies "not a chance". So the owner creates a metal bar and installs it, and names it the Biff bar (or anti Biff bar, whichever way we want to call it).
2) Pinball player strolls into his local arcade in 1955 and fires some quarters into his favourite machine. He death saves time and time again and is going crazy on the machine, and the local patrons are casting a rather evil eye his way. The owner, whose name is Biff, creates a metal bar and installs it to prevent the death save activity on the machine, and thus the "Biff bar" is born.
You are correct, Stern was going all out back in the LOTR days with metal aprons and Biff bars, no expense was spared.