Dead Magic Zones have the opposite problem. They aren’t cast, their area can be huge, and their duration can be infinite. There’s typically no source so they cannot be turned off by attacking something. In other words, they areThat means they’re just pure DM-fiat “you all suck now, and there are no relevant tactical decisions that can do anything about them.” The players may not have any real option
Worse, Dead Magic Zones are highly asymmetric: spellcasters can be left with literally nothing to do, warriors stripped of remedyingmagic items are in a lot of trouble, and plenty of monsters don’t care in the situationleast. So some people are basically told “you don’t get to play, may not” others get “here’s a challenge that you have to complete without any particular tactical options for mitigating itof your usual abilities,” and so on. They may be entirely sidelined becausesome (most normally, the DM said so. If it happened to meenemy) are told: “hey, I’d be strongly questioning if I wanted to continue playing for this DM. I don’t commit my severely-restricted free timeyour enemies have been stripped of most of their ability to roleplay a cheerleader.fight, have fun!”
I therefore suggest not using them at all. If you insist on using them, use them sparingly, and make sure that there are plenty of options for dealing with it. A fight, or series of fights, or a whole dungeon, that takes place entirely within a Dead Magic Zone that has no source and cannot be removed, is boring and poor design. ASome characters may literally be relegated to cheerleader status, without even the Bard’s ability to make his cheers count for something (even if he was a Bard, since Inspire Courage is supernatural).
Instead, a fight where certain key strategic areas are protectedcan be made more interesting by temporary or small Dead Magic Zones projected by chanting circles of cultists, or specially-inscribed runesDead Magic Zones which can be moved, turned on, or whatever? That could be interesting. Just make sureturned off (or which simply do these things automatically, so you usehave to try to predict/time your positioning to take advantage of them carefully/avoid getting screwed by them). This makes the DMZ add tactical dimensions to the situation, rather than detract from them.
Despite the use of the word “tactical” in these points, this isn’t purely about combat. Combat is a major part of Dungeons & Dragons; the overwhelming majority of the rules are related to it, so it gets proportional coverage here. But plenty of non-combat situations are impossible to deal with without magic, as well.
In short, D&D 3.x is extremely high-magic, and after about level 4 or so the game starts assuming that you have it. By the time antimagic field is available, magic is very nearly everything. Removing magic tends to work poorly and has to be done very carefully.
DMZs also work OK as a way of attempting to enforce non-combat solutions to disagreements with NPCs. They could be a great way to force the PCs to actually talk with someone rather than dash their brains out, if said someone is, say, on the far side of a long chasm with a DMZ between them so they cannot fly over it. This is basically an attempt to intentionally use the fact that DMZs prevent regular play in order to force some non-mechanical roleplaying. In some cases, these may be necessary even among good roleplayers, since it's hard to justify, in-character, not just killing the BBEG when he wants to talk, if you have that opportunity.
