The Kingdom of Loathing

For the upper level bears, use prismatic damage. There's a few good sources of that, and it destroys them just fine. If you're currently rolling in the meat profits, buy some prismatic wads and use em, then you got 30 turns of bear smashin'. There are other, better sources but I can't recall them all right now.

EDIT: Ah yes, also the malevolent medallion. There's Hodgman's trenchcoat too, but only so many people have that one.