Cancel the knife if the knifer takes damage during the lunge. Or, make the knife powerless for a set amount of time if shot from within "melee knife range".

Number two would be interesting and something fresh. Just make sure it isnt a one hit kill.

Number three would be ok also.

The two options I would like to see would either be the knife has to be equipped beforehand or the increase in damage at knife range.  If we had more incentive to shoot at knife range I'm sure more people would instead of hitting the button that gives you an instant kill.  The "Knife Vest" perk (or killstreak) sounds decent in theory, but I feel like that would be about as useful in situations as Shades from WaW.

My favorite solution, one that I've always advocated being used with the knife is a system kind of like this:

If you're at full health OR behind the enemy, 1hko. If you've taken any damage or in front of them, it deals 75 damage. This allows stealthy players to utilize the knife for a 1hko, as you would expect them to. It also allows to still remain mostly effective as a "last resort" weapon when you've ran out of ammo completely.

Other than that (assuming that kind of modification is out of the question), then my next personal favorite idea would be something along the lines of:

- Switch Melee to another button (R2 works great in BF3)

- Reduce/remove the lunge. If someone can't knife someone, that's because they're not close enough, that's their own problem IMO. The game shouldn't compensate because the person incorrectly timed their attack. It would be like saying "Close enough" when someone fires next to an enemy instead of at them, and dealing damage anyway.

- Potentially make the utilize an animation similar to BF3 which leaves you largely vulnerable if you run around trying to knife everyone out in the open.

- Allow a perfectly timed "counter knife" to block the incoming knife (similar to killing an Attack Dog with a perfectly timed knife to counter it's bite)

I don't know how feasible some of these are, but they've been some of my favorite ideas in terms of better balancing the melee system in these games.

number three and make it so you can melee with your gun when you dont have the knife equiped and when you melee with your gun it takes 2 hits for the other dude to drop