Ring of polymorph control

If you are wearing (or have eaten) this ring and something causes you to polymorph, then you will be asked "Become what type of monster? [type the name]". You can generally chose then to polymorph into any genocidal monster (and then some).

If you ever face that question "arch lich" is a pretty decent anwser. Large monsters will typically destory your armor.

Rings of polymorph control will also allow you to decline a change in form brought upon by lycanthorpy.