Wearing a dwarvish cloak protects a worn helm from eroding, since the cloak is hooded.

Remove the recharge counter from objects. Most tools can be infinitely recharged, so they don’t need one. For wands, replace the recharge count with a chance of a wand becoming eroded when the wand is recharged, or of exploding if recharged when already eroded.

Not specified what happens for the few items that don’t follow this pattern, such as magic markers and the wand of wishing. For the wand, it will likely work to make the erosion guaranteed the first time, and the explosion guaranteed when it’s already eroded. Magic markers could possibly just be un-rechargeable.

Amulet of protect inventory: negates any erosion, destruction, disintegration, or theft of your items, but every time it does, you take damage.

Don’t allow items to erode past the point where further erosion stops mattering. For instance, a orcish helm can lose at most 1 AC from eroding, so it should not be allowed to become very or thoroughly rusty, whereas plate mail can lose 3 AC from eroding, so it should be allowed to become thoroughly rusty.

Rust dragon, a type of dragon which breathes and makes melee rust attacks. It eats all types of metals. As with other metallic dragons, it is lawful.

An object property “of rust”, applicable to weapons, which causes its target’s gear to rust and, eventually, get destroyed.

If the iron chain connecting you to your ball is corroded or rusted, it is easier for you to break with a hammer.

Extrinsic sources of acid resistance should protect your weapon from passive corrosion attacks, and extrinsic sources of fire resistance protect your armor from taking fire damage.

Dragonhide gear naturally deteriorates gradually over time, and the only way to prevent this is to rub large quantities of gold on it, which destroys the gold.

When a thrown potion of acid hits a creature, it may corrode some corrodable armor of that creature.

Items in a bones pile, in addition to being cursed, could be subject to additional degradation such as erosion, loss of magical charges, or blanking. (Though since a new player will arrive in the bones level apparently immediately after the death, it could be a bit of a stretch to have the items degrade so much.)

New erosion type “moldy”, which can be dealt to inventory items (or possibly only weapons) when meleeing fungi. The mold does not appear instantly and maybe does not even provoke a message when it appears. It does not have multiple erosion levels, only the one “moldy”, but at certain intervals of about a couple hundred turns, moldy items in main inventory or carried containers have a chance of turning another erodable item moldy as well.

It can be fixed by either standard methods of erosion removal, being subject to fire damage, or possibly by smashing a potion of booze on oneself.

Applying a stethoscope to a monster that has a rusting or corroding passive attack erodes it appropriately.

Weapons and armor that generate in shops can be randomly eroded at any erosion level. Perhaps 10% or 20% of items are eroded, the rest are not.

Spell of repair: level 3 matter spell. If wielded weapon is eroded, fixes its erosion. Otherwise, target a random piece of worn armor and fix any erosion it has. At Unskilled, the erosion will only be repaired 1 level at a time; at Basic, 2 levels; at Skilled, 3 levels; and at Expert (maybe) the item will be erodeproofed.

Silver objects are corrodeable but not, of course, rustable.

Non-erodeproof copper items corrode over time.

Scroll of repair: uncursed repairs all levels of erosion on an item of the player’s choice; a blessed scroll repairs all erosion in the player’s inventory; cursed scroll attempts to erode one random item in inventory 1d3 times. If confused and non-cursed, will erosionproof an item of the player’s choice; if confused and cursed, will remove erosionproofing from a random item and then erode it 1d3 times.

The scroll of enchant weapon retains its confused effect of erosionproofing a weapon, but it no longer erosionproofs non-weapons or repairs the weapon. Enchant weapon scrolls are also made much less common, with the probability dumped into the scroll of repair instead.

Artifact unaligned touchstone called Grinder: rubbing it on or applying it to an object repairs one level of rust or corrosion but decreases enchantment by 1 (which can go negative). Invoking it cancels a single object.

Iron and copper items engulfed by gelatinous cubes get corroded in the process.

Gloves that are sufficiently burnt or rotted only protect from touching cockatrice corpses some of the time.

Give potions more side dipping effects:

• Dipping an eroded item in a healing potion repairs erosion on it; 1 level for regular healing, 2 for extra healing, and 3 for full healing. Restore ability will repair all erosion as well.
• Dipping a negatively enchanted item in a restore ability potion reverts it to +0 if the potion is blessed, adds 1 point if uncursed, and does nothing if cursed.
• Dipping an enchantable item in a gain ability potion enchants it (by 1 point, always).
• Dipping an uncharged item (possibly excluding rings) into restore ability has the same effect as uncursed charging it. (Blessed charging cannot be reproduced this way, even if the potion is blessed).

Add un-eroding a dipped item as an additional fountain dip effect.

Water elementals have an active rust attack.

Erosion on rings and amulets makes their effect intermittent.

Enchantments on armor and weapons time out (rather slowly). Also, any erosion damage to a positively enchanted item will be absorbed by that positive enchantment, which then vanishes in proportion to the amount of erosion. Perhaps the enchant scrolls should be made more common or cost less ink to balance this.

Erosion has more than four states, though it still only displays as “eroded”, “very eroded”, or “thoroughly eroded”; different rusting sources can cause different levels of rust (e.g. dipping a long sword in a fountain or getting hit by a rust trap would probably only cause a small amount of rust, whereas a rust monster might cause a lot.) This would enable a more fair way to have things “erode away completely” like they do in Grunthack, since you would be able to disengage any thoroughly eroded piece of gear before it was at serious risk of vanishing.