My DM requires us to say it before the attack roll because the DnDbeyond system rolls the damage at the same time. It doesn't really matter either way on our table because he doesn't nerf the non-lethal damage. So even if I fail to knock it out, it would still do the same damage. 

However, the knock out creature still can die due to bleeding or injury in our table.

I hogtie a knock out an enemy in my last DnD session and want to investigate him later. However, at the end of the battle, my DM tells me that the creature is dead. 

I think you're right.

It's part of why I didn't fight it.

I understand that it's part of player agency, and I have no issue with that.  I just dont' want them deciding after the fact that, "Wait... he was important,.... uh... I was non-lethal"

Has that happened yet?
Actually yes.  That has happened in my campaign.

So that's why my stipulation is that they have to say before they roll attack that it's non-lethal.  If the choice to be non-lethal, then it should be a proactive one, not a reactive one.

And yes, I understand that the rules make that clear.  I just decided to make it a bit more emphatic.

If you're sticking with the rest of the non-lethal rules, I don't see any reason you should have to declare the attack non-lethal ahead of time, declaring it once the DM declares that the damage was sufficient is good enough.  This is because there's only one attack that matters whether it's lethal or not, the final one. 

Now if you wait until after the DM starts narrating the consequences of that person dying, that's a different matter entirely, but that shouldn't really be an issue unless the DM is especially eager or you didn't know you wanted them alive until bad stuff happened.

Personally, I go with the normal non-lethal rules with the addition that ranged attacks can be declared non-lethal as well, but in that case, NPCs can make death saves instead of automatically being stable.

fair enough

i guess my issue is i've got exploiters and rules lawyers in the same group

i just need to git gud and grow a pair

I agree on the crit....Rolling a 20 should be a reward and not a detriment to the goals.

I can't think of many bladed weapons that don't have a handle. It's reasonable to assume that if your trying not to kill someone, you wouldn't cut them with a blade. No reason you couldn't hit them in the head with your pommel though. 

Quote from Grondsmash >>

We found the RAW rule to be utterly stupid.

 

Reality and/or versimilitude must be balanced with utility at the table. 

Or to put it another way, there have to be simple non-lethal rules otherwise the GM has no way to defeat the party except for a TPK. 

This is something I faced in an AD&D 1E game many, many moons ago. How can I capture a party when the players refuse to have their characters surrender? 

Quote from MikCage >>

I can't think of many bladed weapons that don't have a handle. It's reasonable to assume that if your trying not to kill someone, you wouldn't cut them with a blade. No reason you couldn't hit them in the head with your pommel though. 

 Or a flat side of the blade. Or if the opponent have a decent armor/helmet then it doesn't really matter. Just because you hit it, it doesn't mean you have open up a big cut.

In my games, I have decided that a non-lethal attack is declared before rolling damage by not adding their damage modifier to their damage roll.

This way there is a risk when trying to subduing your opponents in a non-lethal manner, which I believe is a necessity when trying to implement the mechanic in a way that makes sense, much as what InquisitiveCoder alluded to in a previous comment. It makes a difference, but not so much that your attacks are anywhere near useless. Another benefit of this is that I have begun reminding my players of this when their attack rolls hit on a very hurt target, and thus simultaneously let my players know the condition their target is in from a (meta)game perspective.

Logically I agree that a non-lethal attack should be declared before the attack roll with a similar penalty, but I have a hard time figuring out how this should work without adding more complexity and a much harder penalty, ultimately making the game less fun for the players.

I haven't experienced any down-sides to my homebrew rule yet (13 sessions in), however feel free to give me your insights if you have tried to implement something similar :)

There is some truth to the range attack exclusion.. because if you want to take them down non-lethaly, the weapons would have to be special.. 
I have a Halfling deputy-sheriff from another Meta-realm.. (rule set) who prefers to use waxed sand bullets.  Which here would be a specific-rule homebrew item.

You don't necessarily need a special weapon, but a DM that houserule it since Knocking a Creature Out normally doesn't work on a ranged attack but on a melee attack, this with or without a weapon.

If it's an important NPC, the players might inquire during combat whether the DM plans to use the Monsters and Death rule from the PHB:

Most DMs have a monster die the instant it drops to 0 hit points, rather than having it fall unconscious and make death saving throws.

Mighty villains and special nonplayer characters are common exceptions; the DM might have them fall unconscious and follow the same rules as player characters.

If so, the party is free to take the NPC out in whatever manner they like and then just stabilize it after it reaches 0 hit points, so long as they don't exceed the damage threshold for death saving throws.

Our group has only run into the "non-lethal after the hit" once, when I didn't explicitly state on the attack it was supposed to be non-lethal.  Our DM, being more alert, remembered our INTENT going in, was to save one enemy, so asked me if I wanted to strike a non-lethal blow.  As a Monk, it was supremely easy to narrate, being an unarmed strike, so a lot of the "realism" mechanics folks have issue with are moot.  Since then, we have stated at the beginning of combat, we intend to take someone alive, so when that target receives it's "killing blow" (our group is 3 melee and once caster) he/she simply falls to the ground unconscious.  I feel stating at the start of the fight you intend to keep someone alive works best, as the DM and party then have a plan and makes it much easier to work the battle a bit more seamlessly.  

I also suggest the following:

A rule from the Hero System, called Cover (not to be confused with being behind an obstacle for improved defense). 

A character rolls damage that would bring an enemy to 0 or less.  The attacker has the option to slay (apply normal damage), knock them out cold as per RAW, or intimidate them into surrendering. 

Assuming the enemy has enough intelligence to comprehend intent, the attacker can withhold damage, with the option to apply damage at will.  This is essentially having a sword to the target's throat, or a gun pointed at them, and offering an opportunity to surrender (drop weapons, lower guard, cease use of armor proficiency).  In the case of a ranged attack, the combatants must be within 15' of each other.  

There is however, a means of escape...with the difficulty set by the attackers Cha bonus (it is a form of intimidation)  plus the roll (including any modifiers) they rolled to hit - a difficult proposition.  The victim can apply his cha bonus + his applicable proficiency bonus (if the target has something handy that might aid in thier escape from being covered).

Success means they've managed to escape from having the damage applied, failure means the attacker is free to instantly apply damage, either slaying them, knocking them out, or continuing

You don't get to decide that a player is unable to control their character like that. Stating the dire wolf druid cannot pull their punches just because you think it is unrealistic entirely removes the player's agency. Why is transforming into another being while maintaining sentience "realistic" enough for you, but them being able to control the force they use not? 

That point about how you envision hit points is key.

Many times, especially in the middle of a fight, people seem to revert to 10 HP = 1 pint of blood or something. But I like how RAW keeps it simple, for one thing, and open to the mental and physical stamina required for staying active in a fight. Or morale. Or any number of other things that a DM can work into the narration.

The other point I'd add goes along with narration.

An earlier post gave examples of a barbarian attacking and ripping arms off and then putting a pinky on his chin to say, "I meant it non-lethally." When I DM, I try to keep it clear that declaring an action and rolling the dice only constitutes what you're planning to do. After the numbers are all added up, then you can negotiate what you actually accomplished. And if that means the PC wants to finish the attack by bopping little dire-bunny FooFoo on the head to knock it out -- all good. D&D is a board game that emphasizes storytelling. A dramatic, collaborative adventure is typically more enjoyable than a precise, rules flowchart.