Anti-grenade grenade.
Don't know how it works, just throw it on the ground where nades are usually spammed and if one lands it just scuttles over and dis-arms it
BTW, I have a few ideas for how to cut down on grenade spam in COD4:
-remove the 3-grenade perk completely
-Grenades alone can only kill with a "close range" hit, otherwise they just temporarily put them in a "last stand" state till they recover.
-shorten detonation time to 3 seconds if they attempt a high arc = explode in mid air (grenade timers are more like randomly 3-5 seconds, not ALWAYS 5 seconds as in COD games)
-Less god damn open space maps, more trenches and cover so a grenade pretty much has to land dead on to explode. Tunnels for example, all over a map, unlocked by kill-streaks or completing objectives.
-Standing water, deep puddles. I know for a fact that grenades are virtually useless if they land in a small amount of water as a bucket.
Strange idea:
-Grenade diver: to level up quickly, if a grenade lands nearby and your team-mates are in danger, press a different key and you dive on the grenade to save your buddies. I think might be useful in search and destroy.
Less good ideas:
-have something like this (http://en.wikipedia.org/wiki/CIWS) on the map that I already know are able to shoot out the sky the much faster moving mortars. maybe upgrade with a high-power laser to zap any high arcing nades out the sky.
-anti-mortar radar: Radar picks up any high arc grenades then automatically launch a missile at that position.
-make the player's throw unusually weak if they attempt a high arc